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POWER STATIONS AND 
TRANSMISSION 


A COMPREHENSIVE TREATISE ON ELECTRIC POWER STATION 
EQUIPMENT, DESIGN, AND MANAGEMENT, AND THE 
* ERECTION AND MAINTENANCE OF PROPER 
TRANSMISSION LINES 


BY ^ 

GEORGE C.^SHAAD, E.E. 

PROFESSOR OF ELECTRICAL ENGINEERING, UNIVERSITY OF KANSAS 


ILLUSTRATED 


AMERICAN TECHNICAL SOCIETY 
CHICAGO 
1917 





TK l \9 I 

. s ^ 


COPYRIGHT, 1913, 1917, BY 
AMERICAN TECHNICAL SOCIETY 


COPYRIGHTED IN GREAT BRITAIN 
ALL RIGHTS RESERVED 



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DEC 17 1917 

©CI.A479561 

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INTRODUCTION 


T HE concentration for economic purposes of the many power 
plants of a large municipality into one immense station 
like that of the Commonwealth Edison Company of Chi¬ 
cago, Illinois, and the utilization of our natural water-power sites 
like Niagara Falls, New York, or the Mississippi River at Keokuk, 
Iowa, show a modern tendency which is becoming more and more 
pronounced every year. 

<1 With the world’s supply of coal supposedly on the wane, atten¬ 
tion has been turned inevitably to the tremendous natural supply 
of energy in our rivers and falls which is going to waste. The suc¬ 
cess of the many plants which have been developed recently has not 
only broadened the interest of engineers and capitalists as to the 
possibilities in long-distance transmission of electricity but has 
added one more subject of spectacular interest to the general public. 
With these developments in mind it seems reasonable to make the 
prediction that the next twenty-five years will see practically all 
these sources of power utilized. 

<1 With the natural increase in the size of the plants have come the 
demands for better design and for more economical machinery and 
management. If the plant is a steam plant, every known element 
of economy in the shape of the latest type of reciprocating engine 
or of high- and low-pressure turbines, boilers of the latest and most 
approved type, with superheaters, condensers, and other economical 
accessories, have been installed. If the plant is hydroelectric, the 
water turbines and all the details in connection with them are worked 
out along the highest engineering principles. In a comparatively 
few years the size of the dynamos has increased from 5,000 kilowatts 
to 20,000 kilowatts and, by transforming the voltage as high as 
110,000 for purposes of transmission, the radius of profitable dis¬ 
tribution of electricity has been very materially increased. 

<J Altogether the subject is one of exceptional interest, and the 
author’s treatment of the important features of power station design, 
approved station equipment, and the methods of transmission 
of the enormously high voltage now used, makes the work a very 
attractive one. Many tables of useful data, wiring diagrams, and 
descriptions of special features have been introduced and will be 
found invaluable to the engineer. The material is admirably adapted 
for purposes of home study and should prove of interest to a wide 
circle of readers. 



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CONTENTS 


PART I 


POWER STATIONS 

PAGE 

Introduction. 1 

Location of station. 2 

Accessibility. 2 

Water supply. 2 

Stability of foundations. 3 

Surroundings. 3 

Facility for extension. 3 

Cost of real estate. 3 

General features. 4 

Miscellaneous considerations. 4 

Selection of system. 5 

Factors in design.;... 7 

Steam plant. 8 

Boilers. 9 

Classification. 9 

Initial cost. 11 

Deterioration. 11 

Floor space. 11 

Efficiency. 11 

Steam piping. 13 

Superheated steam. 18 

Feed water. 19 

Feeding appliances. 20 

Boiler setting. 22 

Draft. 22 

Firing of boilers. 23 

Steam engines. 24 

Steam turbines. 26 

Advantages. 26 

Types. 27 

Hydraulic plant. 31 

Water turbines. 32 

Gas plant. 36 

Electric plant. 38 

Generators. 38 

Transformers. 42 

Storage batteries. 46 

Switchboards. 47 

Panels.,. 49 

Oil switches. 57 











































CONTENTS 


Switchboards— (continued) page 

Safety devices. 61 

Substations. 68 

Buildings. 72 

Foundations. 74 

Station arrangement. 78 

Station records. 79 

Methods of charging for power. 86 


PART II 

POWER TRANSMISSION 

PAGE 

Introduction. 1 

Conductors. 1 

Material. 1 

Resistance. 3 

Current-carrying capacity. 7 

Insulation. 8 

Distribution system (single circuit). 11 

Series. 11 

Parallel.“. 13 

Series-multiple and multiple-series. 18 

Distribution systems (multiple circuit). 18 

Three-wire. 18 

Voltage regulation. 21 

Distribution systems (alternating current). 22 

Series. 22 

Parallel. 23 

Voltage regulation. 23 

Polyphase. 27 

Amount of copper for different systems. 28 

Transmission lines. 29 

Capacity. 29 

Inductance. 30 

Alternating current line calculations. 35 

Transformers. 49 

Power losses. 50 

Efficiency. 50 

Regulation. 52 

Connections. 53 

Choice of frequency. 55 

Overhead lines. 56 

Location of line. 57 

Poles. 58 

Cross-arms. 63 

Insulators. 63 












































CONTENTS 


Overhead lines —(continued) page 

Pins. 66 

Line stresses. 66 

Conductors. 73 

Underground construction . 73 

Systems. 73 

Conduit materials. 76 

Manholes. 78 

Cables.'. 80 

Miscellaneous factors . 83 

Selection of voltage. 83 

Line protection. 84 














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PART I 


POWER STATIONS 

INTRODUCTION 

With the rapid increase of the use of electricity for power, 
lighting, traction, and electro-chemical processes, the power houses 
equipped for the generation of the electrical supply have increased 
in size from plants containing a few low-capacity dynamos, belted 
to their prime movers and lighting a limited district, to the modern 
central station, furnishing power to immense systems and over 
extended areas. Examples of the latter type of station are found 
at Niagara Falls, and such stations as the Metropolitan and Man¬ 
hattan stations in New York City, and the plants of the Boston 
Edison Illuminating Company, etc. 

The subject of the design, operation, and maintenance of cen¬ 
tral stations forms an extended and attractive branch of electrical 
engineering. The design of a successful station requires scientific 
training, extensive experience, and technical ability. Knowledge 
of electrical subjects alone will not suffice, as civil and mechanical 
engineering ability is called into play as well, while ultimate suc¬ 
cess depends largely on financial conditions. Thus, with unlimited 
capital, a station of high ‘economy of operation may be designed 
and constructed, but the business may be such that the fixed charges 
for money invested will more than equal the difference between the 
receipts of the company and the cost of the generation of power 
alone. In such cases it is better to build a cheaper station and one 
not possessing such extremely high economy, but on which the fixed 
charges are so greatly reduced that it may be operated at a profit. 

The designing engineer should be thoroughly familiar with 
the nature and extent of the demand for power and with the prob¬ 
able increase in this demand. Few systems can be completed for 
their ultimate capacity at first and, at the same time, be operated 
economically. Only such generating units, with suitable reserve 
capacity, as are necessary to supply the demand should be installed 


2 


POWER STATIONS 


at first, but all apparatus should be arranged in such a manner that 
future extensions can readily be made. 

Power stations, as here treated, will be considered under the 
following general topics: 

Location of Station 
Steam Plant 
Hydraulic Plant 
Gas Plant 
Electric Plant 
Buildings 
Station Records 

LOCATION OF STATION 

The choice of a site for the generating station is very closely 
connected with the selection of the system to be used, which sys¬ 
tem, in turn, depends largely on the nature of the demand, so that 
it is a little difficult to treat these topics separately. Several possi¬ 
ble sites are often available, and we may either consider the require¬ 
ments of an ideal location, selecting the available one which is 
nearest to this in its characteristics, or we may select the best system 
for a given area and assume that the station may be located where 
it would be best adapted to this system. Wherever the site may 
be, it is possible to select an efficient system, though not always an 
ideal one. 

The points that should be considered in the location of a station, 
no matter what the system used, are accessibility, water supply, 
stability of foundations, surroundings, facility for extension, and 
cost of real estate. 

Accessibility. The station should be readily accessible on ac¬ 
count of the delivery of fuel, of stores, and of machinery. It should 
be so located that ashes and cinders may easily be removed. If 
possible, the station should be located so as to be reached by both 
rail and water, though the former is generally more desirable. If 
the coal can be delivered to the bunkers directly from the cars, the 
very important item of the cost of handling fuel may be greatly 
reduced. Again, the station should be in such a location that it may 
readily be reached by the workmen. 

Water Supply. Cheap and abundant water supply for both 
boilers and condensers is of utmost importance in locating a steam 


POWER STATIONS 


3 


station. The quality of the water supply for the boiler is of more 
importance than the quantity. It should be as free as possible from 
impurities which are liable to corrode the boilers, and for this 
reason water from the town mains is often used, even when other 
water is available, as it is possible to economize in the use of 
water by the selection of proper condensers. The supply for 
condensing purposes should be abundant, otherwise it is necessary 
to install extensive cooling apparatus, which is costly and occupies 
much space. 

Stability of Foundations. The machinery, as well as the buildings, 
must have stable foundations, and it is well to investigate the avail¬ 
ability of such foundations when selecting the site. 

Surroundings. In the operation of a power plant using coal or 
other fuels, certain nuisances arise, such as smoke, noise, vibration, 
etc. For this reason it is preferable to locate where there is little 
liability to complaint on account of these causes, as some of these 
nuisances are costly and difficult, or even impossible, to prevent. 

Facility for Extension. A station should be located where there 
are ample facilities for extension and, while it may not always be 
advisable to purchase land sufficient for these extensions at first, 
if there is the slightest doubt in regard to being able to purchase it 
later, it should be bought at once, as the station should be as free 
as possible from risk of interruption of its plans. Often real estate 
is too high for purchasing a site in the best location, and then the 
next best point must be selected. A consideration of all the factors 
involved is necessary in determining whether or not this cost is too 
high. In densely populated districts it is necessary to economize 
greatly with the space available, but it is generally desirable that 
all the machinery be placed on the ground floor and that adequate 
provision be made for the storage of fuel, etc. 

Cost of Real Estate. The location of substations is usually fixed 
by other conditions than those which determine the site of the main 
power house. Since, in the simple rotary-converter substation, 
neither fuel nor water is necessary, and there is little noise or vibra¬ 
tion, it may be located wherever the cost of real estate will permit, 
provided suitable foundations may be constructed. The distance 
between substations depends entirely on the selection of the system 
and the nature of the service. 


4 


POWER STATIONS 


GENERAL FEATURES 

Miscellaneous Considerations. Where low voltages are used, 
it is essential that the station be located as near the center of the 
system as possible. This center is located as follows: 

Having determined the probable loads and their points of 
application for the proposed system, these loads are indicated on a 
drawing with the location of the same shown to scale. The center 
of gravity of this system, considering each load as a weight, is then 
found and its location is the ideal location, as regards amount of 
copper necessary for the distributing system. 

Consider Fig. 1, which shows the location of five different 





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Fig. 1. Graphical Method of Locating Center of the System 


loads, indicated in this case by the number of amperes. Combining 
loads A and B, we have 

Ax = By x “J- y — a 

Solving these equations, we find that A and B may be considered as 
a load of A + B amperes at F. Similarly, C and D, E and F, and 
G and II may be combined giving us 7, the center of the system. 
The amount of copper necessary for a given regulation runs up 
very rapidly as the distance of the station from this point in¬ 
creases. Where there are obstructions which will not permit the 
feeders to be run in an approximately straight line, the distance 
A B, etc., should be measured along the line the conductors must 
take. 


POWER STATIONS 


5 


Selection of System. General rules only can be stated for the 
selection of a system to be used in any given territory for a certain 
class of service. 

For an area not over two miles square and a site reasonably 
near the center, direct-current, low-pressure, three-wire systems 
may be used for lighting and ordinary power purposes. Either 220 
volts or 440 volts may be used as a maximum voltage, and motors 
should, preferably, be connected across the outside wires of the cir¬ 
cuits. Five-wire systems with 440 volts maximum potential have 
been used, but they require very careful balancing of the load if the 
service is to be satisfactory. 220-volt lamps are giving good satis¬ 
faction; moderate-size, direct-current motors may readily be built 
for this pressure and constant-potential arc lamps may be operated 
on this voltage, though not so economically as on 110 volts, if single 
lamps are used. The new types of incandescent lamps in low candle- 
power units are not suitable for 220 volts. For direct-current rail¬ 
way work, the limit of the distance to which power may be economic¬ 
ally delivered with an initial pressure of 600 volts is from five to 
seven miles, depending on the traffic. 

If the area to be served is materially larger than the above, 
or distances for direct-current railways greater, either of the two 
following schemes may be adopted: (1) Several stations may be 
located in the territory and operated separately or in multiple on 
the various loads; or (2) one large power house may be erected and 
the energy transmitted from this station at a high voltage to various 
transformers or transformer substations which, in turn, transform 
the voltage to one suitable for the receivers. Local conditions usually 
determine which of these two shall be used. The alternating-current 
system with a moderate potential—about 2,300 volts for the primary 
lines—is now often installed for very small lighting systems. 

The use of several low-tension stations operating in multiple 
is recommended only under certain conditions, namely, that the 
demand is very heavy and fairly uniformly distributed throughout 
the area, and suitable sites for the power house can readily be ob¬ 
tained. Such conditions rarely exist and it is a question whether 
or not the single station would not be just as suitable for such cases 
as where the load is not so congested. 

One reason why a large central station is preferred to several 


6 


POWER STATIONS 


smaller stations is that large stations can be operated more eco¬ 
nomically, owing to the fact that large units may be used and they 
can be run more nearly at full load. There is a gain in the cost 
of attendance, and labor-saving devices can be more profitably in¬ 
stalled. The location of the power plant is not determined to such 
a large extent by the position of the load, but other conditions, 
such as water supply, cheap real estate, etc., will be the governing 
factors. In several cities, notably New York, Chicago, and Boston, 
large central stations are being installed to take the place of several 
separate stations, the old stations being changed from generating 
power houses to rotarv-converter substations. Both direct-current 
low-tension machines—for supplying the neighboring districts—and 
high-tension alternating-current machines—for supplying the out, 
lying or residence districts—are often installed in the one station. 

As examples of the central station located at some distance 
from the center of the load, we have nearly all of the large hydraulic 
power developments. Here it is the cheapness of the water power 
which determines the power-house location. The greatest distance 
over which power is transmitted electrically at present is in the 
neighborhood of 200 miles. 

If a high-tension alternating-current system is to be installed, 
there remains the choice of a polyphase or single-phase machine 
as well as the selection of voltage for transmission purposes. As 
pointed out in “Power Transmission,” polyphase generators are 
cheaper than single-phase generators and, if necessary, they can be 
loaded to about 80 per cent of their normal capacity, single-phase, 
while motors can more readily be operated from polyphase circuits. 
If synchronous motors or rotary converters are to be installed, a 
polyphase system is necessary. The voltage will be determined by 
the distance of transmission, care being taken to select a value con¬ 
sidered as standard, if possible. Generators are wound giving a 
voltage at the terminals as high as 15,000 volts, but in many dis¬ 
tricts it is desirable to use step-up transformers for voltages above 
6,600 on account of liability to troubles from lighting. 

With the development of the single-phase railway motor, cen¬ 
tral stations generating single-phase current only, are occasionally 
built in larger sizes than previously, as their use heretofore has been 
limited to lighting stations. 


POWER STATIONS 


7 


Factors in Design. A few general notes in regard to the design 
of plants will be given here, the several points being taken up more 
in detail later. 

Direct driving of apparatus is always superior to methods of 
gearing or belting as it is efficient, safe, and reliable, but it is not as 
flexible as shafting and belts, and on this account its adoption is 
not universal. 

Speeds to be used will depend on the type and size of the gen¬ 
erating unit. Small machines are always cheaper when run at high 
speeds, but the saving is less on large generators. For large engines 
slow speed is always preferable. 

It is desirable that there be a demand for both power and 
lighting, and a station should be constructed which will serve both 
purposes. The use of power will create a day load for a lighting 
station, which does much to increase its ultimate efficiency and, as 
a rule, its earning capacity. 

In addition to generator capacity necessary to supply the load, 
a certain amount of reserve, either in the way of additional units 
or overload capacity, must be installed. The probable load for, say 
three years, can be closely estimated, and this, together with the 
proper reserve, will determine the size of the station. The plant 
as a whole, including all future extensions, should be planned at 
the start as extensions will then be greatly facilitated. Usually it 
will not be desirable to begin extensions for at least three years 
after the first part of the plant has been erected. 

Enough units must be installed so that one or more may be 
laid off for repairs, and there are several arguments in favor of 
making this reserve in the way of overload capacity, for the gen¬ 
erators at least. Some of these arguments are: 

Reserve is often required at short notice, notably in railway plants. 

With overload capacity the rapid increase of load, such as occurs in 
lighting stations when darkness comes on suddenly, may more readily be taken 
care of. 

There is always a-factor of safety in machines not running to their 
fullest capacity. 

Reserve capacity is cheaper in this form than if installed as separate 
machines. 

As a disadvantage, we have a lower efficiency, due to machines not usually 
running at full load, but in the case of generators this is very slight. 


8. 


POWER STATIONS 


TABLE I 

Permissible Overload 33 Per Cent 



Machines added 
one at a time 

Machines added 
two at a time 

Machines added 
three at a time 

No. 

Size. 

No. 

Size. 

No. 

Size. 

Initial installment 

4 

500 

4 

500 

4 

500 

First extension 

1 

666 

2 

1000 

3 

2000 

Second extension 

1 

888 

2 

2000 

5 

5000 

Third extension 

1 

1183 

2 

4000 

4 

5000 

Fourth extension 

1 

1577 

4 

4000 



Fifth extension 

1 

2103 

8 

4000 



Sixth extension 

1 

2804 






With an overload capacity of 33J per cent, four machines should 
be the initial installment, since one can be laid off for repairs, if 
necessary, the total load being readily carried by three machines. 
In planning extensions, the fact that at least one machine may 
require to be laid off at any time should not be lost sight of, while 
the units should be made as large as is conducive to the best opera¬ 
tion. 

Table I is worked out showing the initial installment for a 
2,000-kw. plant with future extensions. It is seen from this table 
that adding two machines at a time gives more uniformity in the 
size of units—a very desirable feature. 

The boilers should be of large units for stations of large capacity, 
while for small stations they must be selected so that at least one 
may be laid off for repairs. 

STEAM PLANT 
BOILERS 

The majority of power stations have as their prime movers 
either steam or water power, though there are many using gas. 
If steam is the power selected, the subject of boilers is one of vital 
importance to the successful operation of central stations. The 
object of the boiler with its furnace is to abstract as much heat as 
possible from the fuel and impart it to the water. The various kinds 
of boilers used for accomplishing this more or less successfully are 
described in books on boilers, and we will consider here the merits 
of a few of the types only as regards central-station operation. 














POWER STATIONS 


9 


The considerations are: (1) Steam must be available through¬ 
out the twenty-four hours, the amount required at different parts 
of the day varying considerably. Thus, in a lighting station, the 
demand from midnight to 6 A. M. is very light, but toward evening, 
when the load on the station increases very rapidly, there is an abrupt 
increase in the rate at which steam must be given off. The maxi¬ 
mum demand can readily be anticipated under normal weather 
conditions, but occasionally this maximum will be equaled or even 
exceeded at unexpected moments. For this reason a certain num¬ 
ber of boilers must be kept under steam constantly, more or less of 
them running with banked fires during light loads. If the boilers 
have a small amount of radiating surface, the loss during idle hours 
will be decreased. 

(2) The boilers must be economical over a large range of 
rates of firing and must be capable of being forced without detriment. 
Boilers should be provided which work economically for the hours 
just preceding and following the maximum load while they may 
be forced, though running at lower efficiency, during the peak. 

(3) Coming to the commercial side of the question, we have 
first cost, cost of maintenance, and space occupied. The first 
cost, as 'does the cost of maintenance, varies with the type and 
the pressure of the boiler. The space occupied enters as a factor 
only when the situation of the station is such that space is limited, 
or when the amount of steam piping becomes excessive. In some 
city-plants, space may be the determining feature in the selection of 
boilers. 

Classification. Boilers for central stations may be classified as 
fire-tube and water-tube types. Of the former may be mentioned 
the Cornish, Lancashire, Galloway, multitubular, marine, and 
economic boilers. The Babcock and Wilcox, Stirling, and Heine 
boilers are examples of the water-tube type. 

Fire-Tube Boilers. The Cornish and Lancashire boilers have 
the fire tubes of such a diameter that the furnaces may be constructed 
inside of them. They differ only in the number of cylindrical tubes 
in which the furnaces are placed, as many as three tubes being placed 
in the largest sizes (seldom used) of the Lancashire boilers. They 
are made up to 200-pound steam pressure and possess the following 
features: 


10 


POWER STATIONS 


1. High efficiency at moderate rates of combustion 

2. Low rate of depreciation 

3. Large water space 

4. Easily cleaned 

5. Large floor space required 

6. Cannot be readily forced 

The Galloway boiler differs from the Lancashire boiler in that 
there are cross-tubes in the flues. 

In the multitubular boiler, the number of tubes is greatly increased 
and their size is diminished. Their heating surface is large and 
they steam rapidly. They require a separate furnace and are used 
extensively for power-station work. 

Marine boilers require no setting. Among their advantages 
and disadvantages may be mentioned: 

1. Exceedingly small space necessary 

2. Radiating surface reduced 

3. Good economy 

4. Heavy and difficult to repair 

5. Unsuitable for bad water 

6. Poor circulation of water 

The economic boiler is a combination of the Lancashire and 
multitubular boilers, as is the marine boiler. It is set in brickwork 
and arranged so that the gases pass under the bottom and along the 
sides of the boiler as well as through the tubes. It way be com¬ 
pared with other boilers from the following points: 

1. Small floor space 

2. Less radiating surface than the Lancashire boiler 

3. Not easily cleaned 

4. Repairs rather expensive 

5. Requires considerable draft 

Water-Tube Boilers. The chief characteristics of the water-tube 
boilers, of which there are many types, are 

1. Moderate floor space 

2. Ability to steam rapidly 

3. Good water circulation 

4. Adapted to high pressure 

5. Easily transported and erected 

6. Easily repaired 

7. Not easily cleaned 

8. Rate of deterioration greater than for Lancashire boiler 

9. Small water space, hence variation in pressure with varying de¬ 

mands for steam 

10. Expensive setting 


POWER STATIONS 


11 


Initial Cost. As regards first cost, boilers installed for 150- 
pound pressure and the same rate of evaporation, will run in the 
following order: Galloway and Marine, highest first cost, Economic, 
Lancashire, and Babcock and Wilcox. The increase of cost, with 
increase of steam pressure, is greatest for the Economic and least 
for the water-tube type. 

Deterioration. Deterioration is less with the Lancashire boiler 
than with the other types. ---- - 

Floor Space. The floor space occupied by these various types 
built for 150 pounds pressure and 7,500 pounds of water, evaporated 
per hour, is given in Table II. 


TABLE II 

Boiler Floor Space 


Kind of Boiler 

Floor Space in sq. ft. 

Lancashire 

408 

Galloway 

371 

Babcock and Wilcox 

200 

Marine wet-back 

120 

Economic 

210 


Efficiency. The percentage of the heat of the fuel utilized by 
the boiler is of great importance, but it is difficult to get reliable 
data in regard to this. Table III* will give some idea of the effi¬ 
ciencies of the different types. The efficiency is more a question of 
proper proportioning of grate and heating surface and condition of 
boiler than of the type of boiler. Economizers were not used in any 
of these tests, but they should always be used with the Lancashire 
type of boiler. 

It is well to select a boiler from 20 to 50 pounds in excess of 
the pressure to be used, as its life may thus be considerably ex¬ 
tended, while, when the boiler is new, the safety valve need not 
be set so near the normal pressure, and there is less steam wasted 
by the blowing off of this valve. Again, a few extra pounds of 
steam may be carried just previous to the time the peak of the 
load is expected. For pressures exceeding 200 or, possibly, 150 
pounds, a water-tube boiler should be selected. 

In large stations, it is preferable to make the boiler units of 


*From Donkin’s “Heat Efficiency of Steam Boilers.” 







12 


POWER STATIONS 


TABLE III 
Boiler Efficiencies 


Kind op Boiler 

No. of Ex¬ 
peri¬ 
ments 

Mean Ef¬ 
ficiency 

OF TWO 

best Ex¬ 
periments 

Lowest 

Effi¬ 

ciency 

Mean Ef¬ 
ficiency 

OF ALL 

Experi¬ 

ments 

Lancashire hand-fired 

107 

79.5 

42.1 

62.3 

Lancashire machine-fired 

40 

73.0 

51.9 

64.2 

Cornish hand-fired 

25 

81.7 

53.0 

68.0 

Babcock and Wilcox hand-fired 

49 

77.5 

50.0 

64.9 

Marine wet-back hand-fired 

6 

69.6 

62.0 

66.0 

Marine dry-back hand-fired 

24 

75.7 

64.7 

69.2 


large capacity, to do away as much as possible with the extra piping 
and fittings necessary for each unit. Water-tube boilers are best 

i 



VALVE. 

Fig. 2. Diagram of Ring System of Piping 

adapted for large sizes. These may be constructed for 150-pound 
pressure, large enough to evaporate 20,000 pounds of water per 
hour, at an economical rate. 













































POWER STATIONS 


13 


Boilers of the multitubular type or water-tube boilers are used 
in the majority of power stations in the United States. For stations 
of moderate size, with medium steam pressures and plenty of space, 
the return tubular boiler is often employed. For the larger stations 
and the higher steam pressures, the water-tube boilers are employed. 
Marine or other special types are used only occasionally where space 
is limited or where other local conditions govern. 

Steam Piping. The piping from the boilers to the engines 
should be given very careful consideration. Steam should be avail- 



ENG1NES 1 BO/LERS 


Fig. 3. Diagram of Ring System with Cross-Connections 

able at all times and for all engines. Freedom from serious inter¬ 
ruptions due to leaks or breaks in the piping is brought about by 
very careful design and the use of good material in construction. 
















































14 


POWER STATIONS 


Duplicate piping is used in many instances. Provision must always 
be made for variations in length of the pipe with variation of tem¬ 
perature. For plants using steam at 150-pound pressure, the varia¬ 
tion in the length of steam pipe may be as high as 2.5 inches for 100 
feet, and at least 2 inches for 100 feet should always be counted 
upon. 

Arrangement. Fig. 2 shows a simple diagram of the ring system, 
of piping. The steam passes from the boiler by two paths to the 
engine and any section of the piping may be cut out by the closing 
of two valves. Simple ring systems have the following characteristics: 

1. The range, as the main pipe is called, must be of uniform size and 
large enough to carry all of the steam when generated at its maximum rate. 

2. A damaged section may disable one boiler or one engine. 

3. Several large valves are required. 

4. Provision may readily be made to allow for expansion of pipes. 

Cross-connecting the ring system, as shown in Fig. 3, changes 
these characteristics as follows: 

1. Size of pipes and consequent radiating surface is reduced. 

2. More valves are needed but they are of smaller size. 

3. Less easy to arrange for expansion of the pipes. 

If the system is to be duplicated, that is, two complete sets of 
main pipes and feeders installed, Fig. 4, two schemes are in use: 

1. Each system is designed to operate the whole station at maximum 
load with normal velocity and loss of pressure in the pipes, and only one system 
is in use at a time. This has the disadvantage that the idle section is liable 
not to be in good operating condition when needed. Large pipes must be 
used for each set of mains. 

2. The two systems may be made large enough to supply steam at nor¬ 
mal loss of pressure when both are used at the same time, while either is made 
large enough to keep the station running should the other section need repairs. 
This has the advantages of less expense, and both sections of pipe are normally 
in use; but it has the disadvantages of more radiating surface to the pipes 
and consequent condensation for the same capacity for furnishing steam. 

Complete interchangeability of units cannot be arranged for 
if the separate engine units exceed 400 to 500 horse-power. Since 
engine units can be made larger than boiler units, it becomes neces¬ 
sary to treat several boiler units as a single unit, or battery, these 
batteries being connected as the single boilers already shown. For 
still larger plants the steam piping, if arranged to supply any engines 
from any batteries of boilers, would be of enormous size. If the 


POWER STATIONS 


15 


boilers do not occupy a greater length of floor space than the engines, 
Fig. 5 shows a good arrangement of units. Any engine can be fed 
from either of two batteries of boilers and the liability of serious 
interruptions of service due to steam pipes or boiler trouble is very 
remote. 

In many plants but a single steam range is used, the station 
depending upon good material, careful construction, and thorough 




n 

i * 
j 1 


i r 

■ i 

i 

i 





T 

__j i _ 

11 
. i 
■ i 
• i 

i: 1 




n- 

11 

11 

. j L 


— 

1 1 






n 

11 
, 1 

1 L 


'll ■ ■ 

1 I 






11 

11 

11 

J L ■ 

- 

- ! r 

! 1 






nr 


Fig. 4. Duplicate System of Piping 


inspection for reliability of service. In the largest steam-turbine 
stations, the so-called unit system is employed as is explained later 
under “Station Arrangement.” 

Material. Steel pipe, lap welded and fastened together by 
means of flanges, is to be recommended for all steam piping. The 
flanges may be screwed on the ends of sections and calked so as to 
render this connection steam tight, though in large sizes it is better 
to have the flanges welded to the pipes. This latter construction 



























































16 


POWER STATIONS 


costs no more for large pipes and is much more reliable. All valves 
and fittings are made in two grades or weights, one for low pressures, 
and the other for high pressures. The high-pressure fittings should 
always be used for electrical stations. Gate valves should always 



BO/LZHS 

Fig. 5. Arrangement of Boilers and Engines 
in Very Large Plants 


be selected, and, in large sizes, they should be provided with a by-pass. 

Asbestos, either alone or with copper rings, vulcanized India 
rubber, asbestos and India rubber, etc., are used for packing between 
flanges to render them steam tight. Where there is much expansion, 
the material selected should be one that possesses considerable 















































POWER STATIONS 


17 


elasticity. Joints for high-pressure systems require much more 
care than those for low-pressure systems, and the number of joints 
should be reduced to a minimum by using long sections of pipe. 

Fittings. A list of the various fittings required for steam piping, 
together with their descriptions, is given in books on boilers. One 
precaution to be taken is to see that such fittings do not become too 
numerous or complicated, and it is well not to depend too much on 
automatic fittings. Steam separators should be large enough to 
serve as a reservoir of steam for the engine and thus equalize, to a 
certain extent, the velocity of flow of steam in the pipes. 

Expansion. In providing for the expansion of pipes due to 
change of temperature, U bends made of steel pipe and having a 
radius of curvature not less than six times, and preferably ten times 
the diameter of the pipe, are preferred. Copper pipes cannot be rec¬ 
ommended for high pressures, while slip expansion joints are most 
undesirable on account of their liability to bind. 

Size. The size of steam pipes is determined by the velocity of 
flow. Probably an average velocity of 60 feet per second would be 
better than 100 feet per second, though in some cases where space 
is limited a velocity as high as 150 feet per second has been used. 

Loss in Pressure. The loss in pressure in steam pipes may be 
obtained from the formula 

QhvL 

Pi lh ~ <?$■ 

where p l — p 2 is the loss in pressure in pounds per square inch; 
Q is the quantity of steam in cubic feet per minute; d is the diame¬ 
ter of pipe in inches; L is the length in feet; w is the weight per 
cubic feet of steam at pressure p 1 and c is a constant, depending 
on size of pipe, values of which for the variation in the size of pipe 
are as follows: 


Diameter of pipe. ¥ 1" 2" 3" 4" 5" 6" 7" 8" 9" 10" 

Value of c . 36.8 45.3 52.7 56.1 57.8 58.4 59.5 60.1 60.7 61.2 61.8 

Diameter of pipe. 12" 14" 16" 18" 20" 22" 24" 

Value of c. .. 62.1 62.3 62.6 62.7 62.9 63.2 63.2 


Mounting. In mounting the steam pipe, it should be fastened 
rigidly at one point, preferably near the center of a long section, and 
allowed a slight motion longitudinally at all other supports. Such 
supports may be provided with rollers to allow for this motion, or 





18 


POWER STATIONS 


the pipe may be suspended from wrought-iron rods which will give 
a flexible support. 

Location. Practice differs in the location of the steam piping, 
some engineers recommending that it be placed underneath the 
engine-room floor and others that it be located high above the engine- 
room floor. In any case it should be made easily accessible, and 
the valves should be located so that nothing will interfere with their 
operation. Proper provision must be made for draining the pipes. 

Lagging. All piping as well as joints should be carefully covered 
with a good quality of lagging as the amount of steam condensed 
in a bare pipe, especially if of any great length, is considerable. In 
selecting a lagging bear in mind that the covering for steam pipes 
should be incombustible, should present a smooth surface, should 
not be damaged easily by vibration or steam, and should have as 
large a resistance to the passage of heat as possible. It must not 
be too thick, otherwise the increased radiating surface will counter¬ 
balance the resistance to the passage of heat. 

The loss of power in steam pipes due to radiation is 

II =.2Q2rLd 

where II is loss of power in heat units; d is diameter of pipe in 
inches; L is the length of pipe in feet; and r is a constant depending 
on steam pressure and pipe covering, values of which for the varia¬ 
tions of these two ^actors are as follows: 


Steam pressure in pounds (absolute). 40 65 90 115 

Values of r for uncovered pipe. 437 555 620 684 

Value of r for pipe covered with 2 inches of 

hair felt.48 58 66 73 


Referring to tables in books on boilers, the relative values of 
different materials used for covering steam pipes may be found. 

Superheated Steam. Superheated steam reduces condensation 
in the engines as well as in the piping, and increases the efficiency 
of the system. Its use was abandoned for several years, due to 
difficulties in lubricating and packing the engine cylinders, but by 
the use of mineral oils and metallic packing, these difficulties have 
been done away with to a large extent, while steam turbines are espe¬ 
cially adapted to the use of superheated steam. The application of 
heat directly to steam, as is done in the superheater, increases the 





POWER STATIONS 


19 


TABLE IV 
Boiler Efficiencies 


Amount of Superheat 

Water Evaporated per Pound 
of Coal 

Without 

Superheat 

With Super¬ 
heat 

40 degrees F. 

7.82 

9.99 

42 degrees F. 

6.42 

7.06 

55 degrees F. 

6.00 

7.00 

56.5 degrees F. 

6.78 

8.66 

55.2 degrees F. 

7.15 

8.65 


efficiency of the boilers. Table IV shows the increase in boiler 
efficiency for a certain boiler test, the results being given in pounds 
of water changed to dry, saturated steam. Tests on various engines 
show a gain in efficiency as high as 9 per cent with a superheat of 
80° to 100° F., while special tests in some cases show even a greater 
gain. 

Superheaters are very simple, consisting of tubular boilers 
containing steam instead of water, and either located so as to utilize 
the heat of the gases, the same as economizers, or separately fired. 
They should be arranged so that they may be readily cut out of 
service, if necessary, and provision must be made for either flooding 
them or turning the hot gases into a by-pass, as the tubes would be 
injured by the heat if they contained neither water nor steam. Su¬ 
perheaters may be mounted in the furnace of the regular boiler set¬ 
ting or they may have furnaces of their own and be separately fired. 
For electrical stations using superheated steam the former type is 
usually employed and it has proved very satisfactory for moderate 
degrees of superheat. 

Feed Water. All water available for the feeding of boilers 
contain some impurities, among the most important of which as 
regards boilers are soluble salts of calcium and magnesium. Bicar¬ 
bonates of the alkaline earths cause precipitations on the interior 
of boilers, forming scale. Sulphate of lime is also deposited by 
concentration under pressure. Scale, when formed, not only de¬ 
creases the efficiency of the boiler but also causes deterioration, 
for if sufficiently thick, the diminished conducting power of the 
boiler allows the tubes or plates to be overheated and to crack or 








20 


POWER STATIONS 


burst. Again, the scale may keep the water from contact w T ith 
sections of the heated plates for some time and then, giving way, 
large volumes of steam are generated very quickly, and an explo¬ 
sion may result. 

Some processes to prevent the formation of scale are used, 
which affect the water after it enters the boilers, but they are not 
to be recommended, and any treatment the water receives should 
affect it previous to its being fed to the boilers. Carbonates and 

a small quantity of sulphate of 
lime may be removed by heat¬ 
ing in a separate, vessel. Large 
quantities of sulphate of lime 
must be precipitated chemic¬ 
ally. 

Sediment must be removed 
by allowing the water to settle. 
Vegetable matters are some¬ 
times present, wdiich cause a 
filin to be deposited. Certain 
gases, in solution—such as oxy¬ 
gen, nitrogen, etc.—cause pit¬ 
ting of the boiler. This effect 
is neutralized by the addition 
of chemicals. Oil from the en¬ 
gine cylinder is particularly de¬ 
structive to boilers and when 
present in the condensed steam 
must be carefully removed. 
Feeding Appliances. Both 
feed pumps and injectors are used for feeding the water to the 
boilers. Feed pumps may be either steam- or motor-driven. Steam- 
driven pumps are very inefficient, but they are simple and the speed 
is easily controlled. Motor-driven pumps are more efficient and 
neater, but more expensive and more difficult to regulate efficiently 
over a wide range of speed. Direct-acting pumps may have feed- 
water heaters attached to them, thus increasing the efficiency of the 
apparatus as a whole. The supply of electrical energy must be 
constant if motor-driven pumps are to be used. 



Fig. 6. Feeding System for Boilers and 
''Pumps' 



















POWER STATIONS 


21 


TABLE V 

Rate of Flow of Water, in Feet per Minute, Through Pipes of 
Various Sizes, for Varying Quantities of Flow 


Gallons 
per Min. 

i in. 

1 IN. 

11 IN. 

li in. 

2 IN. 

2i in. 

3 IN. 

4 IN. 

5 

218 

122| 

78^ 

f 54§ 

CO 

0 

till- 

m 

131 

7f 

10 

436 

245 

157 

109 

61 

38 

27 

15! 

15 

653 

367| 

2351 

163! 

91| 

58 £ 

40| 

23 

20 

872 

490 

314 

218 

122 

78 

54 

30 f 

25 

1090 

612| 

392 i 

272! 

152| 

97i 

67i 

38! 

30 


735 

451 

327 

183 

117 

81 

46 

35 


857| 

549 5 

381! 

213! 

1361 

94i 

53 f 

40 


980 

628 

436 

244 

156 

108 

61| 

45 


1102| 

7061 

490! 

274! 

175| 

1211 

69 

50 



785 

545 

305 

195 

135 

76f 

75 



1177! 

817| 

457! 

292i 

2021 

115 

100 




1090 

610 

380 

270 

153! 

125 





762| 

487-| 

337i 

191f 

160 





915 

585 

405 

230 

175 





10671 

6821 

4721 

268! 

200 





1220 

780 

540 

306! 


Feed pipes must be arranged so as to reduce the risk of fail¬ 
ure to a minimum, and for this reason they are almost always dupli¬ 
cated. More than one water supply is also recommended if there 
is the slightest danger of interruption on this account. One com¬ 
mon arrangement of feed-water apparatus is to install a few large 
pumps supplying either of two mains from which the boiler con¬ 
nections are taken. This is a complicated and costly system of 
piping. A scheme for feeding two boilers where each pump is capable 
of supplying both boilers is shown in Fig. 6. Pipes should be ample 
in cross-section, and, in long lengths, allowance must be made for 
expansion. Cast iron or cast steel is the material used for their con¬ 
struction; the joints being made by means of flanges fitted with 
rubber gaskets. 

The rate of flow of water in feet per minute through pipes of 
various sizes is given in Table V. A flow of 10 gallons per minute 
for each 100 h. p. of boiler equipment should be allowed without 
causing an excessive velocity of flow in the pipes—400 to 600 feet 
per minute represents a fair velocity. 














22 


POWER STATIONS 


Boiler Setting. The economical use of coal depends, to a large 
extent, on the setting of the boiler and proper dimensions of the 
furnaces. Internally-fired boilers require support only, while the 
setting of externally-fired boilers requires provision for the furnaces. 
Common brick, together with fire brick for the lining of portions 
exposed to the hot gases, are used almost invariably for boiler set¬ 
tings. It is customary to set the boiler units up in batteries of 
two, using a 20-inch wall at the sides and a 12-inch wall between 
the two boilers. The instructions for settings furnished by the 
manufacturers should be carefully followed out as they are based 
on conditions which give the best results in the operation of their 
boilers. 

Draft. The best ratio of heating to grate surface for boiler plants > 
depends upon the kind of fuel used and the draft employed. Based 
on a draft of 0.5 inch of water, the following values are given for 
different grades of fuel: 

Pocahontas, W. Va., 45; Youghiogheny, Pa., 48; Hocking Valley, O., 45; 
Big Muddy, Ill., 50; Lackawanna, Pa., No. 1 buckwheat, 32. The first of 
these coals is semi-bituminous, the Lackawanna coal is anthracite, and the other 
coals are bituminous. 

Natural Draft. Natural draft is the most commonly used and 
is the most satisfactory under ordinary circumstances. In deter¬ 
mining the size of the chimney necessary to furnish this draft, the 
following formula is given by Kent: 



where A = area of chimney in sq. ft.; h — height of chimney in ft.; 
and F = pounds of coal per hour. 

The height of chimney should be assumed and the area calcu¬ 
lated, remembering that it is better to have the chimney too large 
than too small. 

The chimney may be either of brick or iron, the latter having 
a less first cost but requiring repairs at frequent intervals. Gen¬ 
eral rules for the design of a brick chimney may be given as follows: 

The external diameter of the base should not be less than T V of the height. 

Foundations must be of the best. 

Interiors should be of uniform section and lined with fire brick. 

An air space must exist between the lining and the chimney proper. 




POWER STATIONS 


23 


The exterior should have a taper of from xe to i inch to the foot. 

Flues should be arranged symmetrically. 

Fig. 7 shows the construction of a brick chimney of good design, 
this chimney being used with 
boilers furnishing engines which 
develop 14,000 h. p. 

Mechanical Draft . Mechan¬ 
ical draft is a term which may 
be used to embrace both forced 
and induced draft. The first 
cost of mechanical-draft systems 
is less than that of a chimney, 
but the operation and repair are 
much more expensive and there 
is always the risk of break-down. 

Artificial draft has the advan¬ 
tage that it can be varied within 
large limits and it can be in¬ 
creased to any desired extent, 
thus allowing the use of low 
grades of coal. 

Firing of Boilers. Coal is 
used for fuel to a greater extent 
than any other material, though 
oil, gas, wood, etc., are used in 
some localities. Local condi¬ 
tions, such as availability, cost, 
etc., should determine the ma¬ 
terial to be used; no general 
rules can be given. From data 
regarding the relative heating 
values of different fuels we find: 
that 1 pound of petroleum, about \ of a gallon, is equivalent, when 
used with boilers, to 1.8 pounds of coal and there is less deteriora¬ 
tion of the furnace with oil; that 7\ to 12 cubic feet of natural 
gas are required as the equivalent of 1 pound of coal, depending on 
the quality of the gas; that 2\ pounds of dry wood is assumed as the 
equivalent of 1 pound of coal. 



GROUND L/HE 


Fig. 7. Good Design of Brick Chimney 
























24 


POWER STATIONS 


Stoking. When coal is used, it requires stoking and this may be 
accomplished either by hand or by means of mechanical stokers, 
many forms of which are available. Mechanical stoking has the 
advantage over hand stoking in that the fuel may be fed to the 
furnace more uniformly, thus avoiding the subjection of the fires 
and boilers to sudden blasts of cold air as is the case when the fire 
doors are opened; in that a poorer grade of coal may be burned, 
if necessary; and in that the trouble due to smoke is much reduced. 
It may be said that mechanical stokers are used almost universally 
in the more important electrical plants. Economic use of fuel requires 
great care in firing, especially if it is done by hand. 

Where gas is used, the firing may be made nearly automatic, 
and the same is true of oil firing, though the latter requires more 
complicated burners, as it is necessary that the oil be vaporized. 

In large stations, operated continuously, it is desirable that, 
as far as possible, all coal and ashes be handled by machinery, though 
the difference in cost of operation should be carefully considered 
before installing extensive coal-handling machinery. Machinery 
for automatically handling the coal will cost from $7.50 to $10 
per horse-power rating of boilers for installation, while the ash- 
handling machinery will cost from $1.50 to $3 per horse-power. 

The coal-handling devices usually consist of chain-operated 
conveyors which hoist the coal from railway cars, barges, etc., to 
overhead bins from which it may be fed to the stokers. The ashes 
may be handled in a similar manner, by means of scraper con¬ 
veyors, or small cars may be used. Either steam or electricity may be 
used for driving this auxiliary apparatus. 

It is always desirable that there be generous provision for the 
storage of fuel sufficient to maintain operations of the plant over 
a temporary failure of supply. 

STEAM ENGINES 

The choice of steam prime movers is one which is governed 
by a number of conditions which can be treated but briefly here. 
The first of these conditions relates to the speed of the engine to 
be used. There is considerable difference of opinion in regard to 
this as both high- and low-speed plants are in operation and are 
giving good satisfaction. Slow-speed engines have a higher first 


POWER STATIONS 


25 


cost and a higher economy. Probably in sizes up to 250 kw., the 
generator should be driven by high-speed engines; from 250 to 
500 kw., the selection of either type will give satisfaction; above 
500 indicated horse-power, the slow-speed type is to be recom¬ 
mended. Drop valves cannot be used with satisfaction for speeds 
above about 100 revolutions per minute, hence high-speed engines 
must use direct-driven valve gears, usually governed by shaft gov¬ 
ernors. Corliss valves are used on nearly all slow-speed engines. 

The steam pressure used should be at least 125 pounds per 
square inch at the throttle and a pressure as high as 150 to 1G0 
pounds is to be preferred. 

Close regulation and uniform angular velocity are required 
for driving generators, especially alternators which are to operate 
in parallel. This means sensitive and active governors, carefully 
designed flywheels, and proper arrangement of cranks when more 
than one is used. 

High-speed engines should not have a speed change greater than 
1§ per cent from no load to full load, but for prime movers used for 
driving large alternators operated in multiple, a speed change as 
great as 4 or 5 per cent may be desirable. The variation in angular 
velocity, where alternators are to be operated in parallel, should 
be within such limits that at no time will the rotating part be 
more than 5V of the pitch angle of two poles from the position 
it would occupy if the angular velocity were uniform at its mean 
value. 

For large engine-driven plants or plants of moderate size, com¬ 
pound condensing engines are almost universally installed. The 
advantage of these engines in increased economy are in part counter¬ 
balanced by higher first cost and increased complications, together 
with the pumps and added water supply necessary for the condensers. 
The approximate saving in amount of steam is shown in Table VI, 
which applies to a 500 horse-power unit. 

Triple expansion engines are seldom used for driving electrical 
machinery, as their advantages under variable loads are doubtful. 
Compound engines may be tandem or cross-compound and either 
horizontal or vertical. The use of cross-compound engines tends 
to produce uniform angular velocity, but the cylinder should be so 
proportioned that the amount of work done by each is nearly equal. 



26 


POWER STATIONS 


TABLE VI 


Engine 

Pounds of Steam 
per H. P. Hour 

Simple non-condensing 

30 

Simple condensing 

22 

Compound non-condensing 

24 

Compound condensing 

16 


A cylinder ratio of about 3§ to 1 will approximate average condi¬ 
tions. Either vertical or horizontal engines may be installed, each 
having its own peculiar advantages. Vertical engines require less 
floor space, while horizontal engines have a better arrangement of 
parts. Either type should be constructed with heavy parts and 
erected on solid foundations. 

Engines should preferably be direct-connected, but this is not 
always feasible, and gearing, belt, or rope drives must be resorted 
to. Countershafts, belt or rope driven, arranged with pulleys 
and belts for the different generators, and with suitable clutches, 
are largely used in small stations. They consume considerable 
power and the bearings require attention. 

Careful attention must be given to the lubrication of all running 
parts, and extensive oil systems are necessary in large plants. In 
such systems a continuous circulation of oil over the bearings and 
through the engine cylinders is maintained by means of oil pumps. 
After passing through the bearings, the machine oil goes to a properly 
arranged oil filter where it is cleaned and then pumped to the bear¬ 
ings again. A similar process is used in cylinder lubrication, the 
oil being collected from the exhaust steam, and only enough new 
oil is added to make up for the slight amount lost. The latter sys¬ 
tem is not installed as frequently as the continuous system for 
bearings. 


STEAM TURBINES 

Advantages. The steam turbine is now very extensively used 
as a prime mover for generators in power stations on account of its 
many advantages, some of which may be stated as follows: 

1 . High steam economy at all loads. 

2 . High steam economy with rapidly fluctuating loads. 







POWER STATIONS 


27 


3. Small floor space per kw. capacity, reducing to a minimum 

the cost of real estate and buildings. 

4. Uniform angular velocity, thus facilitating the parallel 

operation of alternators. 

5. Simplicity in operation and low expense for attendance. 

6 . Freedom from vibration, hence low cost for foundations. 

7. Steam economy is not appreciably impaired by wear or lack 

of adjustment in long service. 

8 . Adaptability to high steam pressures and high superheat 

without difficulty in operation and with consequent im¬ 
provement in economy. 

9. Condensed steam is kept entirely free from oil and can be 

returned to the boilers without passing through an oil 

separator. 

Types. The detailed descriptions of the different types of 
steam turbines are given in books devoted to steam engines and 
turbines and only a small amount of space can be devoted to them 
here. The first classification of steam turbines is into the impulse 
type and the reaction type of turbine. In the impulse type the 
steam is expanded in passing through suitable nozzles and does useful 
work in moving the blades of the rotating part by virtue of its kinetic 
energy. In the reaction type the steam is only partially expanded 
before it comes into contact with the blades and much of the work 
on the moving blades is accomplished by the further expansion of 
the steam and the reaction of the steam as it leaves the blades. Of 
the impulse type the DeLaval and the Curtis turbines are well-known 
makes. The DeLaval turbine is built in small and moderate sizes 
only and is of the single-stage type. The Curtis turbine is built 
in all sizes up to the very largest and is of the multi-stage type. 
The Curtis turbine may be briefly described as follows: 

The Curtis turbine is divided into sections or stages, each 
stage containing one or more sets of stationary vanes and revolving 
buckets. These vanes and buckets are supplied wflth steam which 
passes through suitable nozzles to give it the proper expansion and 
velocity as it issues from the nozzles. By dividing the w T ork into 
stages, the nozzle velocity of the steam is kept down to a moderate 
value in each stage and the energy of the steam is effectively given 
up to the rotating part without excessively high speeds. Fig. 8 


28 


POWER STATIONS 


shows the arrangement of nozzles, buckets, and stationary blades 
or guiding vanes for two stages. A complete turbine of the vertical 
type and of 5,000 kw. capacity is shown in Fig. 9. Governing is 
accomplished by automatically opening or closing some of the nozzles, 


■se&om o 4 ?&&£. 





mmacccccacc 


111 — 

♦ * * 


A/OS 

Mo \s/r->cy o'tfJ 

Stat/or->ar^/ J9 
Mo v'/mgr & /oc/ej 



A/oZ Z /g JD/ojoZ-toac/rn 


Mo vrrtg 23/oafGS 


cco:cccccg:ccccccccccc 




mjLmcmmmim, 


ip^j) j) 


! 


i 


Fig. 8. Diagram of Nozzles and Buckets in Curtis Steam Turbine 


and on overloads the steam may be automatically led directly into 
the second stage of the turbine. The step bearing which supports 
the weight of the rotating part may be lubricated by either oil or 
water under high pressure, this pressure being made great enough 
to support the weight of the moving element on a thin film of the 
lubricant. Only a vertical type of the Curtis turbine is shown here 
but it is also manufactured in the horizontal form. 


























POWER STATIONS 


29 



Of the reaction turbines the Parson's type is the most prominent 
one. It is manufactured in the United States by the Westinghouse 
Machine Company and the Allis-Chalmers Company. An element¬ 
ary drawing of the cross-section of the Allis-Chalmers turbine is 
shown in Fig. 10. Steam enters this turbine at C through the gov¬ 
erning valve D, passes through the opening E, and thence expands 
in its passages through the series of revolving and stationary blades 


Fig. 9. Turbo-Alternator of 5,000 kw. Capacity- 

in the three stages II, J, and K. The steam pressure is balanced 
by means of a series of disks or balance pistons shown at L, M, and 
N. The valve shown at V is automatically opened on overload, 
thus admitting steam directly into stage J. 

The steam economy of the turbine increases with increase in 
vacuum approximately as follows: For every increase in vacuum 
of one inch between 23 inches and 28 inches the increase in economy 
is 3 per cent for 100-kw. units, 4 per cent for 400-kw. units, and 
5 per cent for 1,000-kw. units. This is a greater improvement than 
can be obtained with steam engines under corresponding conditions! 
































































































































































































































































POWER STATIONS 


31 


and the exhaust-steam or low-pressure turbine is being introduced 
to work in conjunction with the reciprocating steam engine, the 
steam expanding down to about atmospheric pressure in the engine 
and continuing down to a high vacuum through the low-pressure 
turbine. A receiver may be introduced between the engine and the 
turbine. A higher steam economy is claimed for such a combina¬ 
tion than could be secured by either engine or turbine alone. 

HYDRAULIC PLANTS 

Because of the relative ease with which electrical energy may 
be transmitted long distances, it has become quite common to locate 
large power stations where 
there is abundant water 
power, and to transmit the 
energy thus generated to 
localities where it is needed. 

This type of plant has been 
developed to the greatest 
extent in the western part 
of the United States, where 
in some cases the trans¬ 
mission lines are very exten¬ 
sive. The power houses now 
completed, or in the course 
of erection at Niagara Falls, 
are examples of the enor¬ 
mous size such stations may 
assume. 

Before deciding to util¬ 
ize water power for driving the machinery in central stations, the 
following points should be noted: 

1. The amount of water power available. 

2. The possible demand for power. 

3. Cost of developing this power as compared with cost of plants using 
other sources of power. 

4. Cost of operation compared with other plants and extent of trans¬ 
mission lines. 

Hydraulic plants are often much more expensive than steam 



Fig. 11. Diagram of Reaction Turbines 

































32 


POWER STATIONS 


plants, but the first cost is more than made up by the saving in 
operating expenses. 

Methods for the development of water powers vary with the 
nature and the amount of the water supply, and they may be studied 
best by considering plants which are in successful operation, each 
one of which has been a special problem in itself. A full descrip¬ 
tion of such plants would be too extensive to be incorporated here, 
but they can be found in the various technical journals. 

Water Turbines. Water turbines used for driving generators 
are of two general classes, reaction turbines and impulse turbines. 



Fis. 12. Pelton Type of Impulse Turbine 


Reaction turbines may be subdivided into parallel-flow, outward- 
flow, and inward-flow types. Parallel-flow turbines are suited for low 
falls, not exceeding 30 feet. Their efficiency is from 70 to 72 per 
cent. Outward-flow and inward-flow turbines give an efficiency 
from 79 to 88 per cent. Impulse turbines are suitable for very high 
falls and should be used from heads exceeding, say, 100 feet, though 
it is difficult to say at what head the reaction turbine would give 
place to the impulse wheel, as reaction turbines are giving good 
satisfaction on heads in the neighborhood of 200 feet, while impulse 
wheels are operated with falls of but 80 feet. A reaction wheel is 
shown in Fig. 11, and the Pelton wheel, one of the best known types 






























POWER STATIONS 


33 


TABLE VII 
Pressure cl Water 


Feet 

Head 

Pressure 
Pounds per 
Sq. In. 

Feet 

Head 

Pressure 
Pounds per 
Sq. In. 

Feet 

Head 

Pressure 
Pounds per 
Sq. In. 

Feet 

Head 

Pressure 
Pounds per 
Sq. In. 

10 

4.33 

105 

45.48 

200 

86.63 

295 

127.78 

15 

6.49 

110 

47.64 

205 

88.80 

300 

129.95 

20 

8.66 

115 

49.81 

210 

90.96 

310 

134.28 

25 

10.82 

120 

51.98 

215 

93.13 

320 

138.62 

30 

12.99 

125 

54.15 

220 

95.30 

330 

142.95 

35 

15.16 

130 

56.31 

225 

97.46 

340 

147.28 

40 

17.32 

135 

58.48 

230 

99.63 

350 

151.61 

45 

19.49 

140 

60.64 

235 

101.79 

360 

155.94 

50 

21.65 

145 

62.81 

240 

103.90 

370 

160.27 

55 

23.82 

150 

64.97 

245 

106.13 

380 

164.61 

60 

25.99 

155 

67.14 

250 

108.29 

390 

168.94 

65 

28.15 

160 

69.31 

255 

110.46 

400 

173.27 

70 

30.32 

165 

71.47 

260 

112.62 

500 

216.58 

75 

32.48 

170 

73.64 

265 

114.79 

600 

259.90 

80 

34.65 

175 

75.80 

270 

116.96 

700 

303.22 

85 

36.82 

180 

77.97 

275 

119.12 

800 

346.54 

90 

'38.98 

185 

80.14 

280 

121.29 

900 

389.86 

95 

41.15 

190 

82.30 

285 

123.45 

1000 

433.18 

100 

43.31 

195 

84.47 

290 

125.62 




of impulse wheels, is shown in Fig. 12. An efficiency as high as 
86 per cent is claimed for the impulse wheel under favorable con¬ 
ditions. The fore bay leading to the flume should be made of such 
size that the velocity of water does not exceed 1J feet per second; 
and it should be free from abrupt turns. The same applies to the 
tailrace. The velocity of water in wooden flumes should not exceed 
7 to 8 feet per second. Riveted steel pipe is used for the penstocks 
and for carrying water from considerable distances under high heads. 
In some locations it is buried, in others it is simply placed on the 
ground. Wooden-stave pipe is used to a large extent when the 
heads do not much exceed 200 feet. In Table VII is given the 
pressure of water in pounds per square inch at different heads, 
while in Table VIII is given considerable data relating to riveted- 
steel hydraulic pipe. Governors of the usual types are required 
to keep the speed of the turbine constant under change of load and 
change of head. 














34 


POWER STATIONS 


TABLE VIII 

Riveted Hydraulic Pipe 


Diam. of 
Pipe in 
Inches 

Area of Pipe 
in Square 
Inches 

Thickness of 
Iron by 
Wire Gauge 

Head in Feet 
the Pipe will 
Safely Stand 

Cu. Ft. Water 
Pipe will Con¬ 
vey per Min. 
at Vel. 3 Ft. 
per Sec. 

Weight per 
Lineal Foot 
in Pounds 

3 

7 

18 

400 

9 

2 

4 

12 

18 

350 

16 

234 

4 

12 

16 

525 

16 

3 

5 

20 

18 

325 

25 

3 34 

5 

20 

16 

500 

25 

4 34 

5 

20 

14 

675 

25 

5 

6 

28 

18 

296 

36 

434 

6 

28 

16 

487 

36 

5% 

6 

28 

14 

743 

36 

734 

7 

38 

18 

254 

50 

5K 

7 

38 

16 

419 

50 

6M 

7 

38 

14 

640 

50 

834 

S 

50 

16 

367 

63 

7 34 

8 

50 

14 

560 

63 

934 

8 

50 

12 

854 

63 

13 

9 

63 

16 

327 

80 

8% 

9 

63 

14 

499 

80 

mi 

9 

63 

12 

761 

80 

1434 

10 

78 

16 

295 

100 

934 

10 

78 

14 

450 

100 

11% 

10 

78 

12 

687 

100 

1524 

10 . 

78 

11 

754 

100 

1734 

10 

78 

10 

900 

100 

19H 

11 

95 

16 

269 

120 

9% 

11 

95 

14 

412 

120 

13 

11 

95 

12 

626 

120 

1734 

11 

95 

11 

687 

120 

1824 

11 

95 

10 

820 

120 

21 

12 

113 

16 

246 

142 

1114 

12 

113 

14 

377 

142 

14 

12 

113 

12 

574 

142 

18% 

12 

113 

11 

630 

142 

1924 

12 

113 

10 

753 

142 

22% 

13 

132 

16 

228 

170 

12 

13 

132 

14 

348 

170 

15 

13 

132 

12 

530 

170 

20 

13 

132 

11 

583 

170 

22 

13 

132 

10 

696 

170 

2434 

14 

153 

16 

211 

200 

13 

14 

153 

14 

324 

200 

16 

14 

153 

12 

494 

200 

2134 

14 

153 

11 

543 

200 

23 34 

14 

153 

10 

648 

200 

26 

15 

176 

16 

197 

225 

1324 

15 

176 

14 

302 

225 

17 

15 

176 

12 

460 

225 

23 

15 

176 * 

11 

507 

225 

2434 

15 

176 

• 10 

606 

225 

28 

16 

201 

16 

185 

255 

1434 

16 

201 

14 

283 

255 

1734 

-16 

201 

12 

432 

255 

2434 

16 

201 

11 

474 

255 

2634 

16 

201 

10 

567 

255 

2934 

















POWER STATIONS 


35 


Riveted Hydraulic Pipe 
(Continued) 


Diam. of 
Pipe in 
Inches 

Area of Pipe 
in Square 
Inches 

Thickness of 
Iron by 
Wire Gauge 

18 - 

254 

16 

18 

254 

.14 

18 

254 

12 

18 

254 

11 

18 

254 

10 

20 

314 

16 

20 

314 

14 

20 

314 

12 

20 

314 

11 

20 

314 

10 

22 

380 

16 

22 

380 

14 

22 

380 

12 

22 

380 

11 

22 

380 

10 

24 

452 

14 

24 

452 

12 

24 

452 

11 

24 

452 

10 

24 

452 

8 

26 

530 

14 

26 

530 

12 

26 

530 

11 

26 

530 

10 

26 

530 

8 

28 

615 

14 

28 

615 

12 

28 

615 

11 

28 

615 

10 

28 

615 

8 

30 

706 

12 

30 

706 

11 

30 

706 

10 

30 

706 

8 

30 

706 . 

7 

36 

1017 

11 

36 

1017 

10 

36 

1017 

8 

36 

1017 

7 

40 

1256 

10 

40 

1256 

8 

40 

1256 

7 

40 

1256 

6 

40 

1256 

4 

42 

1385 

10 

42 

1385 

8 

42 

1385' 

7 

42 

1385 

6 

42 

1385 

4 

42 

1385 

M 

42 

1385 

3 

42 

1385 

5 

16 

42 

1385 

% 


Head in Feet 
the Pipe will 
Safely Stand 

Cu. Ft. Water 
Pipe will Con¬ 
vey per Min. 
at Vel. 3 Ft. 
per Sec. 

Weight per 
Lineal Foot 
in Pounds 

165 

320 

16 % 

252 

320 

20 % 

385 

320 

27% 

424 

320 

30 

505 

320 

34 

148 

400 

18 

227 

400 

22% 

346 

400 

30 

380 

400 

32% 

456 

400 

36% 

135 

480 

20 

206 

480 

24% 

316 

480 

32% 

347 

480 

35% 

415 

480 

40 

188 

570 

27% 

290 

570 

35% 

318 

570 

39 

379 

570 

43% 

466 

570 

53 

175 

670 

29% 

267 

670 

38% 

294 

670 

42 

352 

670 

37 

432 

670 

57% 

102 

775 

31% 

247 

775 

41% 

273 

775 

45 

327 

775 

50% 

400 

775 

61% 

231 

890 

44 

254 

890 

48 

304 

890 

54 

375 

890 

65 

425 

890 

74 

141 

1300 

58 

155 

1300 

67 

192 

1300 

78 

210 

1300 

88 

141 

1600 

71 

174 

1600 

86 

189 

1600 

97 

213 

1600 

108 

250 

1600 

126 

135 

1760 

74% 

165 

1760 

91 

180 

1760 

102 

210 

1760 

114 

240 

1760 

133 

270 

1760 

137 

300 

1760 

145 

321 

1760 

177 

363 

1760 

216 






















36 


POWER STATIONS 


TABLE IX 

Horse=Power per Cubic Foot of Water per Minute for Different Heads 


Heads 

in 

Feet 

Horse- 

Power 

H rads 
in 

Feet 

Horse- 

Power 

Heads 

in 

Feet 

Horse- 

Power 

Heads 

in 

Feet 

Horse- 

Power 

1 

.0016098 

170 

.273666 

330 

.531234 

490 

.788802 

20 

.032196 

180 

.289764 

340 

.547332 

500 

.804900 

30 

.048294 

190 

.305862 

350 

.563430 

520 

.837096 

40 

.064392 

200 

.321960 

360 

.579528 

540 

.869292 

50 

.080490 

210 

.338058 

370 

.595626 

580 

.901483 

60 

.096588 

220 

.354156 

380 

.611724 

580 

.933681 

70 

.112686 

230 

.370254 

390 

.627822 

600 

.965880 

80 

.128784 , 

240 

.386352 

400 

.643920 

650 

1.046370 

90 

.144892 

250 

.402450 

410 

.660018 

700 

1.126860 

100 

.160980 

260 

.418548 

420 

.676116 

750 

1.207350 

110 

.177078 

270 

.434646 

430 

.692214 

800 

1.287840 

120 

.193176 

280 

.450744 

440 

.708312 

900 

1.448820 

130 

.209274 

290 

.466842 

450 

.724410 

1000 

1.609800 

140 

.225372 

300 

.482940 

460 

.740508 

1100 

1.770780 

150 

.241470 

310 

.499038 

470 

.756608 



160 

.257568 

320 

.515136 

480 

.772704 




GAS PLANT 

The gas engine using natural gas, producer gas, blast furnace 
gas, or even illuminating gas in some instances, is being used to a 
considerable extent as a prime mover for electric generators. The 
advantages claimed for the gas engine are: 

1. Minimum fuel and heat consumption. 

2. Low cost of operation and maintenance. 

3. Simplification of equipment and small number of auxiliaries. 

4. No heat lost due to radiation when engines are idle. 

5. Quick starting. 

6. Extensions may be easily made. 

7. High pressures are limited to the engine cylinders. 

As disadvantages of the gas engine may be mentioned the large floor 
space required; small overload capacity; and the heavy and expensive 
foundations necessary. 

Fig. 13 shows the efficiency and amount of gas consumed by 
a 503-h. p. engine, Pittsburg natural gas being used. 


















POWER STATIONS 


37 


The only auxiliaries needed where natural gas is employed are 
the igniter generators and the air compressors—with a pump for the 
picket water in some cases—which may be driven by either a motor 
or a separate gas engine. The jacket water may be utilized for heat¬ 
ing purposes in many plants. Cooling towers may be installed 
where water is scarce. 

Parallel operation of alternators when direct-driven by gas 
engines has been successful, a spring coupling being used between 



Fig. 13. Efficiency Curves of a 500-H. P. Gas Engine 


the engines and the generators in some cases to absorb the variation 
in angular velocity. 

The overload capacity of gas engines depends upon the man¬ 
ner of rating. The ultimate capacity is reached when the engine 
is using a full charge of the best mixture of gas and air at each power 
stroke. Many manufacturers rate their engines at 10 per cent 
below the maximum capacity, thus allowing for a limited amount 
of overload. The gas consumption of gas engines is relatively high 
at loads less than 50 per cent of normal; hence, it is desirable that the 
load be fairly constant and at some value between 50 and 100 per 
cent of the rating of the machine. H. G. Stott has proposed that 
the gas engine be combined with the steam turbine in some electrical 




























































38 


POWER STATIONS 


plants, since the turbine can carry heavy overloads and is fairly 
economical on all loads. In such a plant the steam turbine would 
carry the fluctuations, and arrangements would be made so that the 
gas engine would carry a nearly constant load. 

Gas-producers for gas engines are of two types: the suction 
producer, used for small plants and employing high-grade fuels; 
and the pressure producer, used for the larger units and manufac¬ 
tured for all grades of fuel. 

The fact that no losses occur, due to heat radiation when the 
machines are not running, and the lack of losses in piping, add 
greatly to the plant efficiency. If producer gas or blast-furnace 
gas is used, a larger engine must be installed to give the same power 
than when natural or ordinary coal gas is used. Electric stations 
are often combined with gas works, and gas engines can be installed 
in such stations to particular advantage in many cases. 

In addition to the gas engine, other forms of internal com¬ 
bustion engines, such as oil engines and gasoline engines, are being 
used to a limited extent in small stations. 

ELECTRIC PLANT 

GENERATORS 

The first thing to be considered in the electric plant is the 
generators, after which the auxiliary apparatus in the way of ex¬ 
citers, controlling switches, safety devices, etc., will be taken up. 
A general rule which, by the way, applies to almost all machinery for 
power stations, is to select apparatus which is considered as “stand¬ 
ard” by the manufacturing companies. This rule should be fol¬ 
lowed for two reasons: First, reliable companies employ men who 
may be considered as experts in the design of their machines, and 
their best designs are the ones which are standardized. Second, 
standard apparatus is from 15 to 25 per cent cheaper than semi¬ 
standard or special work, owing to larger production, and it can be 
furnished on much shorter notice. Again, repair parts are more 
cheaply and readily obtained. 

Specifications should call for performance, and details should 
be left, to a very large extent, to the manufacturers. Following 
are some of the matters which may be incorporated in the specifi¬ 
cations for generators: 


POWER STATIONS 


39 


1. Type and general characteristics. 

2. Capacity and overload with heating limits. 

3. Commercial efficiency at various loads. 

4. Excitation. 

5. Speed and regulation. 

6. Mechanical features. 

Types. The type of machine will be determined by the sys¬ 
tem selected. Generators may be direct-current or alternating- 5 
current—single or polyphase—or as in some plants now in operation, 
they may be double-current. The voltage, compounding, frequency, 
etc., should be stated. Direct-current machines are seldom wound 
for a voltage above 600, but alternating-current generators may 
be purchased which will give-as high as 15,000 volts at the terminals. 
As a rule it is well not to use an extremely high voltage for the 
generators themselves, but to use step-up transformers in case a 
very high line voltage is necessary. Up to about 7,000 volts, gen¬ 
erators may be safely used directly on the line. Above this, local 
conditions will decide whether to connect the machine directly to 
the line or to step up the voltage. Machines wound for high potential 
are more expensive for the same capacity and efficiency, but the 
cost of step-up transformers and the losses in the same are saved 
by using such machines, so that there is a slight gain in efficiency 
which may be utilized in better regulation of the system, or in lighter 
construction of the line. On the other hand, lightning troubles are 
liable to be aggravated when transformers are not used, as the 
transformers act as additional protection to the machines, and if the 
transformers are injured they may be more readily repaired or 
replaced. 

The following voltages are considered standard: Direct-current 
generators 125, 250, 550-600. Alternating-current systems, high 
pressure, 2,200, 6,600, 11,000, 22,000, 33,000, 44,000, 66,000, 88,000, 
and 110,000. The generators, when used with transformers, should 
be capable of giving a no-load voltage 10 per cent in excess of these 
figures. Twenty-five and 60 cycles are considered as standard fre¬ 
quencies, the former being more desirable for railway work and the 
latter for lighting purposes. 

Capacity. The size of machines to be chosen has been briefly 
considered. Alternators are rated for non-inductive load or a power 



40 


POWER STATIONS 


TABLE X 

Average Maximum Efficiencies 


Kw. 

Per Cent 

Kw. 

Per Cent 

5 

85 

150 

93 

10 

88 

200 

94 

25 

90 

500 

95 

50 

92 

1000 

96 


factor of unity unless a different power factor is distinctly stated. 
Aside from the overload capacity to be counted upon as reserve, 
the Standardization Report of the American Institute of Electrical 
Engineers recommends the following for the heating limits and 
overload capacity of generators: 

Maximum Values of Temperature Elevation 
Field and armature, by resistance, 50° C. 

Commutator and collector rings and brushes, by thermometer, 55° C. 
Bearings and other parts of machine, by thermometer, 40° C. 

Overload capacity should be 25 per cent for two hours, with 
a temperature rise not to exceed 15 degrees above full load values, 
the machine to be at constant temperature reached under normal 
load, before the overload is applied. A momentary overload of 
50 per cent should be permissible without excessive sparking or 
injury. Some companies recommend an overload capacity of 50 
per cent for two hours when the machines are to be used for railway 
purposes. The above temperature increases are based upon a room- 
temperature of 25° C. 

Efficiency. As a rule, generators should have a high efficiency 
over a considerable range of load, although much depends upon 
the nature of the load. It is always desirable that maximum 
efficiency be as high as is compatible with economic investment. 

Table X gives reasonable efficiencies which may be expected 
for generating apparatus. In order to arrive at what may be con¬ 
sidered the best maximum efficiency to be chosen, the cost of power 
generation must be known, or estimated; and the fixed charges on 
capital invested must also be a known quantity. From the cost 
of power, the saving on each per cent increase in efficiency can be 
determined, and this should be compared with the charges on the 










POWER STATIONS 


41 


TABLE XI 

Exciters for Single-Phase Alternating-Current Generators 

60 Cycles 


Alternator Classificaton 

Exciter Classification 

Poles 

Kw. 

Speed 

Poles 

Kw. 

Speed 

8 

60 

900 

2 

1.5 

1,900 

8 

90 

900 

2 

1.5 

1.900 

8 

120 

900 

2 

1.5 

1,900 

12 

180 

600 

2 

2.5 

1,900 

16 

300 

450 

2 

4.5 

1,800 


additional investment necessary to secure this increased efficiency. 
A certain point will be found where the sum of the two will be a 
minimum. 

If a generator is to be run for a considerable time at light loads, 
one with low “no-load” losses should be chosen. These losses are 
not rigidly fixed but they vary slightly with change of load. It is 
the same question of “all-day efficiency” which is treated, in the 
case of transformers, in “Power Transmission.” Under no-load 
losses may be considered, in shunt-wound generators, friction losses, 
core losses, and shunt-field losses. I 2 R losses in the series field, in 
the armature, and in the brushes, vary as the square of the load. 

Excitation. Dynamos, if for direct current, may be self-excited, 
shunt-wound, compound-wound, or separately excited. Separate 
excitation is not recommended for these machines. Alternators 
require separate excitation, though they may be compounded by 
using a portion of the armature current when rectified by a commu¬ 
tator. Automatic regulation of voltage is always desirable, hence, the 
general use of compound-wound machines for direct currents. Many 
alternators using rectified currents in series fields for keeping the 
voltage nearly constant are in service in small plants, as well as 
several of the so-called “compensated” alternators, arranged with 
special devices which maintain the same compounding with different 
power factors. The latter machine gives good satisfaction if properly 
cared for, but an automatic regulator, governed by the generator 
voltage and current, which acts directly on the exciter field, is taking 
its place. This regulator, known as the Tirrill regulator, is de¬ 
scribed under “Power Transmission.” The capacity of the exciters 













42 


POWER STATIONS 


must be such that they will furnish sufficient excitation to maintain 
normal voltage at the terminals of the generators when running at 
50 per cent overload. Table XI gives the proper capacity of exciters 
for the generators listed. On account of the fact that the speed at 
which the unit runs is an important factor in the excitation required, 
no general figure can be given. 

Exciters may be either direct-connected or belted to the shaft 
of the machine which they excite, or they may be separately driven. 

They are usually compound- 
wound and furnish current at- 
125 or 250 volts. Separately- 
driven exciters are preferred for 
most plants as they furnish a 
more flexible system, and any 
drop in the speed of the gen¬ 
erator does not affect the ex¬ 
citer voltage. Ample reserve 
capacity of exciters should be 
installed, and in some cases 
storage batteries, used in con¬ 
junction with exciters, are rec¬ 
ommended in order to insure 
reliability of service. 

Speed and Regulation. If 
direct-connected, the speeds of the generators will be determined by 
the prime mover selected. If belt-driven, small machines may be run 
at a high speed, as high-speed machines are cheaper than slow- or 
moderate-speed generators. In large sizes, this saving is not so great. 

When shunt-wound dynamos are used, the inherent regula¬ 
tion should not exceed 2 to 3 per cent for large machines. For alterna¬ 
tors, this is much greater and depends on the power factor of the 
load. A fair value for the regulation of alternators on non-inductive 
load is 10 per cent. 

Mechanical Features. Motor-generator sets, boosters, frequency 
changers, and other rotating devices come under the head of special 
apparatus and are governed by the same general rules as generators. 

Transformers. Transformers for stepping the voltage from 
that generated by the machine up to the desired line voltage, or 


























































POWER STATIONS 


43 


vice versd, at the substation, may be of three general types, accord¬ 
ing to the method of cooling. Large transformers require artificial 
means of cooling, if they are not to be too bulky and expensive. They 
may be air-cooled, oil-cooled, or water-cooled. 



Fig. 15. Oil-Cooled Transformer 


Air-cooled transformers, Fig. 14, are usually mounted over an 
air-tight pit fitted with one or more motor-driven blowers which feed 
into the pit. The transformer coils are subdivided so that no part 
of the winding is at a great distance from air and the iron is pro¬ 
vided with ducts. Separate dampers control the amount of air 
which passes between the coils or through the iron. Such trans¬ 
formers give good satisfaction for voltages up to 20,000 or higher, 
and can be built for any capacity. Care must be taken to see that 














44 


POWER STATIONS 


there is no liability of the air supply failing, as the capacity of the 
transformers is greatly reduced when not supplied with air. 





Fig. 16. Water-Cooled Transformer 


Oil-cooled transformers, Fig. 15, have their cores and windings 
placed in a large tank filled with oil. The oil serves to conduct the 
heat to the case, and the case is usually made either of corrugated 
sheet metal or of cast iron containing deep grooves, so'as to increase 
the radiating surface. These transformers do not require such heavy 





POWER STATIONS 


45 


insulation on the outside of the coils as air-blast machi les because 
the oil serves this purpose. Simple oil-cooled transformers are 
seldom built for capacities exceeding 250 kw. as they become too 
bulky, but they are employed for the highest voltages now in use. 



Fig. 17. 400-Kw. Water-Cooled Oil Transformer 


Water-cooled, transformers , Figs. 16 and 17, are used when high 
voltages are required. This type is like an oil-cooled transformer, but 
with water tubes arranged in coils in the top. Cold water passes 
through these tubes and aids in removing heat from the oil. Some 
types have the low-tension windings made up of tubes through which 
the water circulates. Water-cooled transformers must not have 
the supply of cooling water shut off for any length of time when 
under normal load or they will overheat. 




46 


POWER STATIONS 


One or more spare transformers should always be on hand and 
they should be arranged so that they can be put into service on 
very short notice. 



Fig. 18. Three-Phase Aii-Blast Transformeis. Total Capacity, 3,000 Kw. 

Three-phase transformers allow a considerable saving in floor 
space, as shown by a comparison of the machines in Figs. 18 and 


r 





ifi Oi ITT 





f 



^ V ^ vy¥v\ 



Fig. 19. Single-Phase Air-Blast Transformers. Total Capacity, 3,000 Kw. 


19. They are cheaper than three separate transformers which make 
up the same capacity, but they are not as flexible as a single-phase 
transformer and one complete unit must be held for a reserve or 
“spare” transformer. 

Storage Batteries. The use of storage batteries for central 
stations and substations is clearly outlined in “Storage Batteries.” 






































































































































































































































































POWER STATIONS 


47 


The chief points of advantage are: 

1. Reduction in fuel consumption due to the generating machinery 
being run at its greatest economy. 

2. Better voltage regulation. 

3. Increased reserve capacity and less liability to interruption of service. 

The main disadvantage is the high first cost and depreciation. 

SWITCHBOARDS 

The switchboard is the most vital part of the whole system of 
supply, and should receive consideration as such. Its objects are: to 
collect the energy as supplied by the generators and to direct it to 
the desired feeders, either overhead or underground; to furnish a 
support for the various measuring instruments connected in service, 
as well as the safety devices for the protection of the generating ap¬ 
paratus; and to control the pressure of the supply. Some of the 
essential features of all switchboards are: 

1. The apparatus and supports must be fire-proof. 

2. The conducting parts must not overheat. 

3. Parts must be easily accessible. 

4. Live parts except for low potentials must not be placed on the front 
of the operating panels. 

5. The arrangement of circuits must be symmetrical and as simple 
as it is convenient to make them. 

6. Apparatus must be arranged so that it is impossible to make a wrong 
connection that would lead to serious results. 

7. It should be arranged so that extensions may be readily made. 

There are two general types—in the first, all of the switching 
and indicating apparatus is mounted directly on panels; and in the 
second, the current-carrying parts are at some distance from the 
panels, the switches being controlled by long connecting rods, or else 
operated electrically or by means of compressed air. The first may 
again be divided into direct-current and alternating-current switch¬ 
boards. It is from the first class of apparatus that the switchboard 
gets its name and the term is still applied, even when the board 
proper forms the smallest part of the equipment. The term “switch- 
gear” is now being introduced to cover all of the apparatus con¬ 
nected with the switching operations and the term “switchboard” is 
being reserved for the panels and their apparatus only. Switchboards 
have been standardized to the extent that standard generator, ex¬ 
citer, feeder, and motor panels may be purchased for certain classes 


48 


POWER STATIONS 



Three-Conductor Cable Without Joints 
Wiped Joint /nsut atton- 


Alberene Soapstone 
On Wood 

C 




Extra /nsuiaiion 

x=sjsa 


Three-Conductor Cable With Joints 




VOLTS 

A 

B 

C 

D 

E 

F 

6,600 

1 

12 

5 

i 

8 


1 

13,200 

n 

15 

8 

1 

4 

4 

2 

26,400 

2 

19 

14 

1 

2 

7 

4 


i-inch Lead or jVinch Brass Bells 


Fig. 20. Part Section—Showing Cable Bells in Place 










































































































POWER STATIONS 


49 


of work, but the vast majority of them are made up as semi-standard 
or special. 

The leads which carry the current from the machines to the 
switches should be put in with very careful consideration. Their 
size should be such that they will not heat excessively when carry¬ 
ing the rated overload of the machine, and they should preferably 
be placed in fire-proof ducts, although low-potential leads do not 
always require this construction. Curves showing sizes for lead- 
covered cables for different currents are given in “Power Trans¬ 
mission.” Table XII gives standard sizes of wires and cables to¬ 
gether with the thickness of insulation necessary for different voltages. 
Cables should be kept separate as far as possible so that if a fault 
does occur on one cable, neighboring conductors will not be injured. 
For lamp and instrument wiring, such as leads to potential and 
current transformers, the following sizes of wire are recommended: 
No. 16 or No. 14, wiring to lamp sockets. 

No. 12 wire, rubber insulation, all other small wiring under 600 volts po¬ 
tential. 

No. 12, $ 2 " rubber insulation for primaries of potential transformers from 
600 to 3,500 volts. 

No. 8, yz " rubber insulation for primaries of potential transformers up to 
6,600 volts. 

No. 8, yz " rubber insulation for primaries of potential transformers up to 
10,000 volts. 

No. 4, II" rubber insulation for primaries of potential transformers up to 
15,000 volts. 

No. 4, If" rubber insulation for primaries of potential transformers up to 
20,000 volts. 

No. 4, it" rubber insulation for primaries of potential transformers up to 
25,000 volts. 

Where high-tension cables leave their metallic shields they 
are liable to puncture, so that the sheath should be flared out at this 
point and the insulation increased by the addition of compound. 
Fig. 20 shows such cable bells, as they are called, as are recommended 
by the General Electric Company. Other types of cable outlets are 
introduced from time to time. A very excellent type makes use of 
porcelain sleeve for each conductor at the point when it leaves the 
lead sheath. 

Panels. Central-station switchboards are usually constructed 
of panels about 90 inches high, from 16 inches to 36 inches wide, and 
inches to 2 inches thick. Such panels are made of blue Vermont, 


50 


POWER STATIONS 


TABLE XII 


Standard Wire 

(Solid) 


Area 

Diameter 

Terminal 

Amperes 

Thickness 

of Rubber Insulation 

Gauge 

Inches 

Drilling 

Volts 


Circular 

Mils 

Bare 

Drill 

Number 

Constant 

Current 

Capacity 

O 

O 

CD 

3,500 

6,600 

o 

o 

o 

o 

H 

15,000 

20,000 

25,000 

B. & S. 

2,582 

.051 

30 

4 








16 

4,106 

.064 

30 

6 

6T 







14 

6,530 

.081 

30 

10 

3 

in 

3 

32 






12 

16,510 

.128 

18 

25 

3 

64 

3 

32 

5 

32 

7 

32 




8 

26,251 

.162 

5 

40 

A 







6 

41,743 

.204 

i 

4 

60 

1 

16 

JL 

32 

5 

7 

32 

u 

1 4 
3U 

17 

32 

4 

66,373 

.257 

5 

T6 

90 

1 

16 







2 

83,695 

.289 

11 

32 

110 

5 

64 







1 

105,593 

.325 

3 

8 

130 

5 

m 

3 

32 

5 

3 2 

7 

32 

2 1 

64 

1 4 
3 2 

1 7 
32 

0 

133,079 

.365 

7 

16 

170 

5 

64 







00 

167,805 

.410 

15 

3? 

205 

5 

64 







000 

211,600 

.460 

1 7 

TT2 

250 

5 

64 

3 

32 

5 

32 

7 

32 

2 1 

6 4 

14 
3 2 

1 7 
32 

0000 


Standard Cable 

(Stranded) 


Circular 

Mils 

Diameter, 

Inches 

Bare 

Terminal 

Drilling 

Inches 

Con. Cur. 
Capacity 
Amperes 

Thickness of Rubber 
Insulation 
(For 6000 V. only ) 

250,000 

.568 

5 

8 

290 

3 

32 

300,000 

.637 

23 

32 

240 

3 

32 

350,000 

.680 

3 

4 

380 

3 

TZ 

400,000 

.735 

1 3 

1 6 

420 

3 

32 

500,000 

.820 

29 

32 

500 

3 

3? 

600,000 

.900 

1 

575 

7 

64 

800,000 

1.037 

u 

710 

7 

64 

1,000,000 

1.157 

H 

830 

7 

64 

1,500,000 

1.412 


1100 

1 

8 

2,000,000 

1.65 

if 

1350 

1 

8 


pink Tennessee, or white Italian marble, or of black enameled or 
oiled slate. Slate is not recommended for voltages exceeding 1,100. 
The panels are made in two or three parts. When made in two parts, 
the sub-base is from 24 to 28 inches high. They are polished on the 
front and the edges are beveled. Angle and tee bars or pipe work, 
together with foot irons and tie rods, form the supports for such 
panels, and on these panels are mounted the instruments, main 
























































POWER STATIONS 


51 


switches, or controlling apparatus for the main switches, as the case 
may be, together with relays and hand wheels for rheostats and 
regulators. 

The usual arrangement of the panels is to have a separate 
panel for each generator, exciter, arid feeder, together with what 
known as a station or total¬ 


is 



output panel. In order to 
facilitate extensions and 
simplify connections, the 
feeder panels are located 
at one end of the board, the 
generator panels are placed 
at the other end, ancl the 
total-output panel occupies 
a position between the two. 

The main bus bars extend 
throughout the length of 
the generator and feeder 
panels, and the desired con¬ 
nections are readily made. 

The instruments required 

are very numerous. Lists of meters required for standard practice 
and regular panels are given later. 

For direct-current generator panels or for the direct-current side 
of synchronous converters , two-wire system, there are usually required: 


Fig. 21. Wiring Diagram of D. C. Generator I’aiel 


1 Main switch 
1 Field switch 
1 Ammeter 
1 Voltmeter 

1 Field rheostat with controlling mechanism 
1 Circuit breaker 

1 4-point starting switch (for use when machine is to be started as a 
direct-current motor). 

Bus bars and various connections. 


These may be arranged in any suitable order, the circuit breaker 
being preferably located at the top so that any arcing which may 
occur will not injure other instruments. Fig. 21 gives a wiring dia¬ 
gram of such a panel. 

The main switch may be a single- or a double-throw, depending on 
whether one or two sets of bus bars are used. It may be a triple- 




























52 


POWER STATIONS 


pole, as shown in Fig. 21, in which the middle bar serves as the equal¬ 
izing switch, or the equalizing switch may be mounted on a pedestal 
near the machine, in which case the generator switch would be 
double-pole. 

The field switch for large machines should be double-pole fitted 
with carbon breaks and arranged with a discharge resistance con¬ 
sisting of a resistance which is thrown across the terminals of the 



Fig. 22. Carbon Break Circuit Breaker 


field just before the main circuit is opened. One voltmeter located 
on a swinging bracket at the end of the panel, and arranged so that 
it can be thrown across any machine or across the bus bars by means 
of a dial switch, is sometimes used, but it is preferable to have a sep¬ 
arate meter for each generator. 





POWER STATIONS 


53 


Small rheostats are mounted on the back of the panel, but 
large ones are chain-operated and preferably located below the floor, 
the controlling hand wheel being mounted on the panel. 

The circuit breaker may be of the carbon break or the magnetic 
blow-out type. Figs. 22 and 23 show circuit breakers of these types. 
Lighting panels for low potentials are often fitted with fuses instead of 
circuit breakers, in which case they may be open fuses on the back 



Fig. 23. Magnetic Blow-Out Circuit Breaker 


of the panel or enclosed fuses on either the front or back of the 
panel. 

A panel for a direct-current generator or a synchronous converter 
for a 3-wire system should contain: 

2 Ammeters. 

2 Circuit breakers. Fuses use! on 3^ 1 ° ’ .tors. 






54 


POWER STATIONS 


3 Single-pole switches, double-throw if there are two sets of bus bars. For 
a three-wire generator or a synchronous converter two single-pole or one 
double-pole switch may be used, in which case the neutral wire is not 
brought to the switchboard. 

2 Hand-wheels for the field rheostats. But one required if a three-wire gen¬ 
erator is used but the two are necessary if the three-wire system is ob¬ 
tained by the use of two generators or a balancer set. 

2 Field switches. But one is required for a three-wire generator or synchronous 
converter. 

1 Four-point starting switch. Required only when the machine is to be 

started as a direct-current motor at times. 

2 Potential receptacles, four-point, used in connection with a voltmeter, 

usually mounted on a swinging bracket. Only one is required for the 
three-wire generator or the synchronous converter. 

An alternating-current generator or a synchronous motor panel 
for a three-phase, three-wire system will require: 

3 Ammeters. Only one required for a single-phase panel or for a synchronous 

motor. 

1 Three-phase indicating wattmeter. 

1 Voltmeter. 

1 8-point potential receptacle used to connect the above voltmeter across 
any phase. Not necessary for the synchronous motor. 

1 Field ammeter. Convenient but not always necessary. 

1 Double-pole field switch with discharge clips. 

1 Hand-wheel for field rheostat. 

1 Synchronizing receptacle. 

1 Triple-pole oil switch, usually non-automatic for generators but automatic 
for motors. This may be single-or double-throw, depending upon the 
bus bar arrangements. 

1 Synchronizer. A single instrument may serve for several machines. 

2 Current transformers. 

2 Potential transformers. Only one necessary for motor. 

1 Power Factor indicator. Not always necessary. 

1 Governor control switch. Not always necessary. 

Where the switches are of the remote control type, the control 
switches or the operating handles are mounted on the panel. 

A three-phase induction-motor panel should contain: 

1 Ammeter. 

1 Automatic oil switch, preferably operated by means of an inverse time¬ 
limit relay. 

The starting compensator used with induction motors is usually mounted 
independently of the switchboard panel. 

The instruments used on a synchronous converter panel, alternat¬ 
ing-current control, are: 


POWER STATIONS 


55 


1 Ammeter. 

1 Synchronizing receptacle. 

1 Oil-switch, automatic. 

1 Potential transformer. 

2 Current transformers. 

1 Switch for control of regulator where a regulator is used and operated by 
means of a small motor. 

A three-phase feeder panel requires: 

3 Ammeters. In some cases only one is necessary. 

1 Automatic oil switch. 

2 Current transformers. 

1 Potential Transformer. Not always needed. 

1 Voltmeter. Not always needed. 

1 Hand-wheel for control of regulator where a regulator is used. 



Direct-Current feeder panels contain: 

1 Ammeter. Two are required for a 3-wire feeder. 

1 Circuit breaker, single-pole. Two are required for a 3-wire feeder. 

1 or more main switches, single-pole or double-pole, and single- or double¬ 
throw, depending upon the number of bus bars. 

1 Recording wattmeter, not always used. 

1 Potential receptacle. 

Apparatus for controlling regulators when such are used. 

One voltmeter usually serves for several feeder panels, such a 
meter being mounted above the panels or on a swinging bracket 
at the end. Switches should preferably be of the quick-break type. 
Figs. 24 and 25 show some standard switchboard panels as manu¬ 
factured by the General Electric Company. 




























56 


POWER STATIONS 


Exciter panels are nothing more than generator panels on a 
small scale. The necessary instruments for a panel controlling one 
exciter are: 

1 Ammeter. 

1 Field rheostat. 

1 Voltmeter. 

1 3-pole switch with fuses. 

1 4-point potential receptacle. 

1 Equalizing rheostat. This is necessary only where a Tirrill regulator is used 
and more than one exciter is operated on the same set of excitation buses. 


(SYNCHRONISM IND/CA TOR 


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MAINF/ELD 

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SW/TCj 


'ITCH 

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CONTROL 

SWITCH 


WON-AUTO 
MAT/C O/L 
SWITCH 


AUTOMATIC 

OILSWITCH 


’hANEFLA, 


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JLL) L 


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125 V 
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susses p, 

RECORDING P 
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TRANSFORMER V 

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SECT/O/y THROUGH 
SYNCHRONOUS MOTORRAN EL 

L 



Fig. 25. Standard Switchboard Panel 


Total Output Panels contain instruments recording the total 
power delivered by the plant to the switchboard. The paralleling 
of alternators is treated in “Management of Dynamo Electric Ma¬ 
chinery.” 

For the higher voltages on alternating-current boards, the meas¬ 
uring instruments are no longer connected directly in the circuit, 
and the main switch is not mounted directly on the panel. Current 







































































POWER STATIONS 


57 


and potential transformers, as called for in the lists given in connec¬ 
tion with the different panels, are used for connecting to the indi¬ 
cating voltmeters and the ammeters and the recording wattmeters, 
and potential transformers are used for the synchronizing device. 



Fig. 26. Three-Phase Oil Switch with Oil Container Removed 


These transformers are mounted at some distance from the panel, 
while the switches may be located near the panel and operated by a 
system of levers, or they may be located at a considerable distance 
and operated by electricity or by compressed air. 

Oil Switches. Oil switches are recommended for all high po¬ 
tential work for the following reasons: 

By their use it is possible to open circuits of higher potential and carry¬ 
ing greater currents than with any other type of switch. 


58 


POWER STATIONS 


They may be made quite compact. 

They may readily be made automatic and thus serve as circuit breakers 
for the protection of machines and circuits when overloaded. 

There are several types of oil switches on the market. A switch 
constructed for three-phase work, to be closed by hand and to be 



Fig. 27. Three-Phase Oil Switch with Oil Container in Place 


electrically tripped or opened by hand, is shown in Fig. 26. This 
shows the switch without the can containing the oil. Fig. 27 shows 
a similar switch hand-operated, with the can in place. Both of 
these switches are arranged to be mounted on the panel. Fig. 28 
shows how the same switches are mounted when placed at some dis¬ 
tance from the panel. For high voltages, they are placed in brick 












POWER STATIONS 


59 





y 


' <r«< <*< Mm** ■</««««< 


kj 




lol 


"6. 


i 


f 


n 


lol 


Jron Pvper 


\Oj 




Fig. 28. Four Arrangements of Oil Switch when Mounted at Some Distance from 

the Panel 

























































































































































































































































































60 


POWER STATIONS 


cells and often three separate single-pole switches are used, each 
placed in a separate cell so that injury to the contacts in one leg will in 
no way affect the other parts of the switch. A form of oil switch 
used for the higher potentials and currents met with in practice, 
is shown in Fig. 29. This particular switch is operated by 
means of an electric motor, though it may as readily be arranged to 
operate by means of a solenoid or by compressed air. General 



Fig. 29. Form of Oil Switch for High Potentials 


practice is to place all high-tension bus bars and circuits in separate 
compartments formed by brick or cement, and duplicate bus bars 
are quite common. 

Oil switches are made automatic by means of tripping mag¬ 
nets, which are connected in the secondary circuits of current trans¬ 
formers, or they may be operated by means of relays fed from the 
secondaries of current transformers in the main leads. Such relays 
are made very compact and can be mounted on the front or back 
of the switchboard panels. The wiring of such tripping devices is 
shown in Fig. 30. 













































































POWER STATIONS 


61 


SOURCE 


CURRENT 

TRANSFORMERS 


0/E SW/TCH 


!l>^! 




OVERLOAD , 
CO/E — 


LOAD 


With remote control of switches, the switchboard becomes in 
many instances more properly a switch house, a separate build¬ 
ing being devoted to the bus bars, 
switches and connections. In 
other cases a framework of angle 
bars or gas pipe is made for the 
support of the switches, bus bars, 
current and potential transform¬ 
ers, etc. The supports for the 
controlling switches are some¬ 
times mounted in a nearly hori¬ 
zontal position, forming the bench 
type of control board. 

Additional types of panels 
which may be mentioned are 
transformer panels, usually con¬ 
taining switching apparatus only, 
and arc-board panels. The latter 
are arranged to operate with plug 
switches. A single panel used in 
the operation of series transform¬ 
ers on arc-lighting circuits is 
shown in Fig. 31. 

Safety Devices. In addition 
to the ordinary overload tripping 
devices which have already been 
considered, there are various 
safety devices necessary in con¬ 
nection with the operation of cen¬ 
tral stations. One of the most 
important of these is the light¬ 
ning arrester. For direct-current 
work, the lightning arrester often 
takes the form of a single gap con¬ 
nected in series with a high resist¬ 
ance and fitted with some device for destroying the arc formed by 
discharge to the ground. One of these is connected between either 
side of the circuit and the ground, as shown diagrammatically in 



C/RCU/T NORMALLY CLOSED 



TO CONT/NUOUS 
CURRENT SUPPLY 

Fig. 30. Wiring Diagram for Tripping 
Devices 



























































62 


POWER STATIONS 


Fig. 32. A “kicking” coil is connected in circuit between the ar¬ 
resters and the machine to be protected, to aid in forcing the lightning 
discharge across the gap. In railway feeder panels such kicking 
coils are mounted on the backs of the panels. 



Fig. 31. Single Panel for Series Transformers in Arc-Lighting Circuits 


For alternating-current work, several, gaps may be arranged in 
series, these gaps being formed between cylinders of “non-arcing” 
metal. High resistances and reactance coils are used with these, 
as in direct-current arresters. Fig. 33 shows connections for a 10,000- 
volt lightning arrester. The resistance used in connection with 
lightning arresters are of special design and non-inductive. In recent 
















POWER STATIONS 


63 


types these resistances are connected in shunt to the gaps as shown in 
Fig. 34. Lightning arresters should always be provided with 
knife blade switches so that they can be disconnected from the cir¬ 
cuit for inspection and repairs. A typical installation of lightning 
arresters is shown in Fig. 35. 


Connections Cor. Senes Arc Lighting Circuits, up to 6000 Vo/ts^ 


GfttEFA TOE5 




iConnections Cor Fat/wag Circuits up to 850 Vo its. [One side Grounded) 
FfACTAt/Cf CO/L 


Gf/YfFATOF 


0 


X 


Feaction Coil is 
Composed of F5 ft- 
of Conductor Wound 
in a Coii of Two or 
More Turns as Con 
venient. 



Fig. 32. Lightning-Arrester Diagrams of D. C. Work 


In place of a series of gaps a single gap with terminals made in 
the form of horns is employed in some cases for lightning protection. 
Such an arrester is known as a horn gap, or horn arrester. The gap 
is connected between the line and the ground and when the po¬ 
tential strain becomes great enough the gap is broken down. The 
arc formed by the machine current after the gap is broken down 












































64 


POWER STATIONS 



Fig. 33. Connections for 10,000-Volt Lightning Arrester 







































































































POWER STATIONS 


65 



Fig. 35. Typical Installation of Lightning Arresters 























































































66 


POWER STATIONS 


rises and lengthens until it can no longer be maintained by the gen¬ 
erator or generators in service. The horn arrester as applied to series 
lighting circuits is shown in Fig. 36. A series resistance, shown in 
the lower part of the figure, is used with this particular arrester. 


The most recent develop¬ 
ment in the way of light¬ 
ning protection is the intro¬ 
duction of the aluminum 
cell arrester. The elemen¬ 
tary cell consists of two 
aluminum plates, on which 
a film of aluminum hydrox¬ 
ide is formed, and which 
are immersed in a suitable 
electrolyte. The peculiar 
property of such a cell 
which makes it useful as 
a lightning arrester is that 



Fig. 36. “Horn” Lightning Arrester 


it has a high resistance up to a certain potential impressed upon 
it but when a critical value of voltage is reached, the resistance be¬ 
comes very low. The critical voltage for a single unit for alternating 
current is between 335 and 360 volts, and such a cell may be con¬ 
nected to a 300-volt circuit with only a very small current flow. 
For higher voltages, a number of cells are connected in series and 
a horn gap is inserted between the arrester and the line wire. The 
gap prevents any flow of current unless the arrester is brought into 
action by the discharge of excess line potential, in which case the 
aluminum cells offer a path of low resistance for the discharge of 
potential so long as the voltage is in excess of the critical voltage, 
but the machine or line potential, which is below the critical voltage 
of the arrester, cannot force enough current through the arrester 
circuit to maintain the arc at the gap. There is some dissolution 
of the film of hydroxide if the cell is left standing and not connected 
to the circuit, but it is readily formed again when the circuit is made. 
Arresters using a gap should have the gap closed for a short in¬ 
terval daily in order to insure a proper film on the aluminum plates. 
Views of the aluminum arrester are shown in Figs. 37 and 38. 

Reverse-current relays are installed when machines or lines 





POWER STATIONS 


67 


are operated in parallel. If two or more alternators are running and 
connected to the same set of bus bars, and one of these should fail 
to generate voltage by the opening of the field circuit, or some other 
cause, the other machine would feed into this generator and might 
cause considerable damage before the current flowing would be 
sufficient to operate the circuit breaker by means of the overload trip 
coils. To avoid this, reverse-current relays are used. They are so 



Fig. 37. Installation of Aluminum Lightning Arrester for 35,000 Volts 


arranged as to operate at, say \ the normal current of the machine or 
line, but to operate only when the power is being delivered in the 
w T rong direction. 

Speed-limit devices are used on both engines and rotary con¬ 
verters to prevent racing in the one case and running away in the 
second. Such devices act on the steam supply of engines and on 
the direct-current circuit breakers of rotary converters, respectively. 

Complete wiring diagrams for standard switchboards are shown 
in Figs. 39 and 40. 






































68 


POWER STATIONS 


SUBSTATIONS 

Substations are for the purpose of transforming the high poten¬ 
tials down to such potentials as can be used on motors or lamps, 
and in many cases to convert alternating current into direct current. 

Step-down transformers do not differ in 
any respect from step-up transformers. 
Either motor-generator sets or rotary 
converters may be used to change from 
alternating to direct current. The for¬ 
mer consist of synchronous or induction 
motors, direct connected to direct-current 
generators, mounted on the same bed¬ 
plate. The generator may be shunt or 
compound wound, as desired. Rotary 
or synchronous converters are direct- 
current generators, though specially de¬ 
signed ; and they are fitted with collector 
rings attached to the winding at definite 
points. The alternating current is fed 
into these rings and the machine runs 
as a synchronous motor, while direct 
current is delivered at the commutator end. There is a fixed re¬ 
lation between the voltage applied to the alternating-current side 
and the direct-current voltage, which depends on the shape of the 
wave form, losses in the armature, pole pitch of the machine, method 
of connection, etc. The generally accepted values are given in 
Table XIII. 

The increase of capacity of six-phase machines over other 
machines of the same size is given in Table XIV. 

This increase is due to the fact that, with a greater number of 
phases, less of the winding is traversed by the current which passes 
through the converter. The saving by increasing the number of 
phases beyond six is but slight and the system becomes too complex. 
Rotary converters may be over-compounded by the addition of 
series fields, provided the reactance in the alternating circuits be 
of a proper value. It is customary to insert reactance coils in the 
leads from the low-tension side of the step-down transformers to the 
collector rings to bring the total reactance to a value which will insure 


TV HORN CAP 

PORCELA // 
BOSH/NS 

METAL COVER 


F/BER 

/NSULAT/ON 

Ti/BE 


O/L 
ELECTRO/ > 

CONES /N 
CROSS 
SECT/ON 
A/UM/NUM 
CONES 
COMPLETE 



Fig. 38. Cross-Section of 
Aluminum Arrester 




























Fig. 39. Wiring Diagram for Standard Switchboard 










































































































































































































Fig. 40. Wiring Diagram for Standard Switchboard 
























































































































































































































































































































POWER STATIONS 


71 


TABLE XIII 
Full Load Ratios 


Current 

Potential 

Per Cent, 

Continuous 

100 

Two-phase ( 550 volts 

72.5 

and Six-phase j 250 volts 

73 

(diametrical) 1125 volts 

73.5 

Three-phase r 550 volts 

62 

and Six-phase } 250 volts 

62 

(Y or delta) ( 125 volts 

63 


the desired compounding. Again, the voltage may be controlled 
by means of induction regulators placed in the alternating-current 
leads. 

Two other methods of potential regulation for synchronous 
converters are in use. In the first of these methods a series gener¬ 
ator is used, this generator consisting of a polyphase armature at¬ 
tached to the rotary converter shaft and revolving in a separate 
field. The phases of this armature are connected between the col¬ 
lector rings of the machine and the taps to the converter armature, 
and the voltage impressed upon the converter taps amounts to the 
line voltage plus or minus the potential developed in the regulating 
armature. By means of a suitable field rheostat for the regulating 
field, any ordinary range of direct current at the brushes of the con¬ 
verter can be obtained with a constant voltage of alternating-current 
supply. Fig. 41 shows a converter equipped with this regulating 
device. 

In the regulating-pole converter each pole of the machine is 
made up of two parts, the main pole and the regulating pole. By 


TABLE XIV 
Capacity Ratios 


Continuous-current generator 

100 

Single-phase converter 

85 

Two-phase converter 

164 

Three-phase converter 

134 

Six-phase converter 

196 








72 


POWER STATIONS 



varying the excitation of the regulating pole the ratio of conversion 
between the alternating-current voltage and the direct-current 
voltage can be changed through a considerable range—a sufficient 
range to cover the requirements ordinarily required in practice. 
Fig. 42 shows a view of a regulating pole converter. Motor-gen¬ 
erators are more costly and occupy more space than rotary con¬ 
verters but the regulation of the voltage is much better and they 
are to be preferred for lighting purposes. 

BUILDINGS 

The power station usually has a building devoted entirely to 
this work, while the substations, if small, are often made a part or 


other buildings. While the detail of design and construction of the 
buildings for power plants belongs primarily to the architect, it is 
the duty of the electrical engineer to arrange the machinery to the 
best advantage, and he should always be consulted in regard to the 
general plans, at least, as this may save much time and expense in 
the way of necessary modifications. The general arrangement of 
the machinery will be taken up later, but a few points in connection 


Fig. 41. Rotary Converter Equipped with Regulating Generator 


POWER STATIONS 


73 


with the construction of the buildings and foundations will be con¬ 
sidered here. 

Space must be provided for the boilers—this may be a sepa¬ 
rate building—engine and dynamo room, general and private offices, 
store rooms and repair shops. Very careful consideration should 
be given to each of these departments. The boiler room should be 
parallel with the engine room, so as to reduce the necessary amount 
of steam piping to a minimum, and if both rooms are in the same 
building a brick wall should separate the two, no openings which 
would allow dirt to come from the boiler room to the engine room 
being allowed. The height of both boiler and engine rooms should 



Fig. 42. Regulating-Pole Rotary Converter 


be such as to allow ample headway for lifting machinery and space 
for placing and repairing boilers, while provision should be made for 
extending these rooms in at least one direction. Both engine and 
boiler rooms should be fitted with proper traveling cranes to fa¬ 
cilitate the handling of the units. In some cases the engines and 
dynamos occupy separate rooms, but this is not general prac¬ 
tice. Ample light is necessary, especially in the engine rooms. The 
size of the offices, store rooms, etc., will depend entirely on local 
conditions. 



74 


POWER STATIONS 


TABLE XV 

Thickness of Walls for Power Plants 


Width of 
Building 
clear 

BETWEEN 

WALLS 

Height 

of 

Wall 

First Section 

Second Section 

Third Section 

Height 

Thickness 

Height 

Thickness 

Height 

Thickness 

25 feet 

40 feet 

40 feet 

12 inches 





25 feet 

40 60 feet 

40 feet 

16 inches 

To top 

12 inches 



25 feet 

60-75 feet 

25 feet 

20 inches 

To top 

16 inches 



25 feet 

75-85 feet 

20 feet 

24 inches 

20-60 ft. 

20 inches 

To top 

16 inches 

25 feet 

85-100 ft. 

25 feet 

28 inches 

25-50 ft. 

24 inches 

50-75 feet 

20 inches 


Note. With clear space exceeding 25 feet the walls should be made 4 
inches thicker for each 10 feet or fraction thereof in excess of 25 feet. For 
buildings greater than 100 feet in height, each additional 25 feet or fraction 
thereof next above the curb shall be increased 4 inches in thickness. 

Foundations. The foundations for both the walls and the ma¬ 
chinery must be of the very best. It is well to excavate the entire 
space under the engine room to a depth of eight to ten feet so as to 
form a basement, while in most cases the excavations must be made 
to a greater depth for the walls. Foundation trenches are sometimes 
filled with concrete to a depth sufficient to form a good underfoot¬ 
ing. The area of the foundation footing should be great enough 
to keep the pressure within a safe limit for the quality of the soil. 
The walls themselves may be of wood, brick, stone, or concrete. 
Wood is used for very small stations only, while brick may be used 
alone or in conjunction with steel framing, the lattei 1 construction 
being used to a considerable extent. If brick alone is used, the walls 
should never be less than twelve inches thick, and eighteen to twenty 
inches is better for large buildings. They must be amply reinforced 
with pilasters. Stone is used only for the most expensive stations. 

Table XV, which is taken from the New T York Building Laws, 
may serve as a guide to the thickness of walls for power plants. 
The interior of the walls is formed of glazed brick, when the expense 
of such construction is ^warranted. In fireproof construction, which 
is always desirable for power stations, the roofs are supported by 
steel trusses and take a great variety of forms. Fig. 43 shows what 
has been recommended as standard construction for lighting stations, 
showing both brick and wood construction. The floors of the engine 














POWER STATIONS 


75 


room should beimade of some material which will not form grit or 
dust. Hard tile, unglazed, set in cement or wood floors, is desirable. 
Storage battery rooms should be separate from all others and should 
have their interior lined with some material which will not be affected 
by the acid fumes. The best of ventilation is desirable for all parts 
of the station, but is of particular importance in the dynamo room 
if the machines are being heavily loaded. Substation construction 
does not differ from that of central stations when a separate build¬ 
ing is erected. They should be fireproof if possible. 

The foundations for machinery should be entirely separate 
from those of the building. Not only must the foundations be 



Fig. 43. Standard Construction for Lighting Station. Brick and Wood Construction 


stable, but in some locations it is particularly desirable that no 
vibrations be transmitted to adjoining rooms and buildings. A 
loose or sandy soil does not transmit such vibrations readily, but 
firm earth or rock transmits them almost perfectly. Sand, wool, 
hair, felt, mineral wool, and asphaltum concrete are some of the 
materials used to prevent this. The excavation for the foundation is 
made from 2 to 3 feet deeper and 2 to 3 feet wider on all sides, than 
the foundation, and the sand, or whatever material is used, occupies 
this extra sptce. 
































76 


POWER STATIONS 



Fig. 44. Foundation for Machines Showing Use of Template and Iron Pipe for Hold¬ 
ing Bolts 



QE/YTE F 'OF DtYF FTd _ 


4«S^f*— f— 3 *" 



YYote ■ 

For brief foundation a /Zin foot¬ 
ing of concrete shou/d be /aid. 
Depth of foundation must be govern¬ 
ed by the character of the sod 
Batter f to e. 

Foundation timbers and f/oormg 
Shou/d be independent of station 
f/oor. 


Fig. 45. Foundation for 150-Kw. Generator 






















































































































































































































































































































































































































POWER STATIONS 


77 


Brick, stone, or concrete is used for building up the greater 
part of machinery foundations, the machines being held in place 
by means of bolts fastened in masonry. A template, giving the 



>T 

For Sr/cA foundation a rZ mch "ily 
roof mg of concrete should be 
laid. Depth of foundation must 
be governed by the characit- 
of the •soft. Batter f to 6 


It BOLTS 


tz BOLT 







Fig. 46. Foundation for Rotary Converter 


location of all bolts to be used in holding the machine in place, 
should be furnished, and the bolts may be run inside of iron pipes 
with an internal diameter a little greater than the diameter of the 




I ^ e 

m - —q 

I 1 i ^3 

ENGINES DYNAMOS 

| SJY/TOHJiOARp 

BO/LED HOUSE ~~ ENG/HE DOOM 



BOILER ROOM ENG/HE ROOM 


Fig. 47. Diagram of Simple Arrange- Fig. 48. Diagram of Arrangement of 

ment of Belted Machines Machines Using Jack Shaft 


bolt. This allows some play to the bolt and is convenient for the 
final alignment of the machine. Fig. 44 gives an idea of this con¬ 
struction. The brickwork should consist of hard-burned brick of 
the best quality, and should be laid in cement mortar. It is well 
to fit brick or concrete foundations wfith a stone cap, forming a 
level surface on which to set the machinery, though this is not neces- 


































































78 


POWER STATIONS, 


sary. Generators are sometimes mounted on wood bases to furnish 
insulation for the frame. Fig. 45 shows the foundation for a 150- 
kw. generator, while Fig. 46 shows the foundation for a rotary 
converter. 

Station Arrangement. A few points have already been noted 
in regard to station arrangement, but the importance of the sub¬ 
ject demands a little further consider¬ 
ation. Station arrangement depends 
chiefly upon two facts—the location and 
the machinery to be installed. Un¬ 
doubtedly the best arrangement is with 
all of the machinery on one floor with, 
perhaps, the operating switchboard 
mounted on a gallery so that the at¬ 
tendants may have a clear view of all 
the machines. Fig. 47 shows the sim¬ 
plest arrangement of a plant using 
belted machines. Fig. 48 shows an arrangement of units where a 
jack shaft is used. Direct-current machines should be placed so 
that the brushes and commutators are easily accessible and the 

switchboard should be placed so 



Fig. 49. Diagram of Double-Deck 
Arrangement of Machines 


as not to be liable to accidents, 
such as the breaking of a belt or 
a flywheel. 

When the cost of real estate 
prohibits the placing of all of the 
machinery on one floor, the en-. 
gines may be placed on the first 
floor and belted to generators on 
the second floor, Fig. 49. It is 
always desirable to have the en¬ 
gines oil the main floor, as they 
cause considerable vibration when 
not mounted on the best of 
foundations. The boilers, while 
heavy, do not cause such vibration and they may be placed on the 
second or third floor. Belts should not be run vertically, as they 
must be stretched too tightly to prevent slipping. 



Fig. 50. Diagram of Station Using Direct- 
Connected Units 


























POWER STATIONS 


79 


Fig. 50 shows a large station using direct-connected units, while 
Figs. 51 and 52 show the arrangement of the turbine plant of the 
Boston Edison Electric Illuminating Company. This station will 
contain twelve large turbine units when completed. Note the arrange¬ 
ment of boilers when several units are required for a single prime mover. 

The use of the steam turbine has led to the introduction of a 
type of station known as a double-deck power plant and used in some 
instances where it is desirable to save space. In this type of sta¬ 
tion the boilers are placed on the ground floor and the turbines, 
which are of the horizontal type, are placed on a second floor directly 
above the boilers. Since there is but little vibration to the turbines 
and only light foundations are necessary, this construction may be 
readily carried out. Fig. 53 shows the general arrangement of 
such a plant. The use of a separate room or building for the cables, 
switches, and operating boards is becoming quite common for high- 
tension generating plants. The remarkable saving in floor space 
brought about by the turbine is readily seen from Fig. 54. The total 
floor space, occupied by the 5,000 kw. units of the Boston station 
is 2.64 square feet per kw. This includes boilers—of which there 
are eight, each 512 h. p. for each unit—turbines, generators, switches, 
and all auxiliary apparatus. For the 10,000 and 15,000 kw. turbine 
sets now coming into use, this figure is still further reduced. 

When transformers are used for raising the voltage, they may 
be placed in a separate building, as is the case at Niagara Falls, or 
the transformers may be located in some part of the dynamo room, 
preferably in a line parallel to the generators. 

Fig. 55 shows the arrangement of units in a hydraulic plant. 
Fig. 56 is a good example of the practice in substation arrange¬ 
ment. The switchboard is at one end of the room, while the 
rotary converters and transformers are along either side. 

Large cable vaults are installed at the stations operating on 
underground systems, the separate ducts being spread out, and sheet- 
iron partitions erected to prevent damage being done to cables which 
were not originally defective, by a short circuit [in any one feeder. 

Station Records. In order to accurately determine the cost of 
generating power and to check up on uneconomical or improper 
methods of operation and lead to their improvement, accurately- 
kept station records are of the utmost importance. Such records 


80 


POWER STATIONS 



Fig. 51. Part Section of Turbine Plant. Boston Edison Luminating Company 


































































































































































































Fig. 52. Plan of Turbines of Fig. 51 

































































82 


POWER STATIONS 


should consist of switchboard records, engine-room records, boiler- 
room records, and distributing-system records. Such records a^ 
curately kept and properly plotted in the form of curves, serve ad ¬ 
mirably for the comparison of station operations from day to day 
and for the same periods for different years. It pays to keep these 
records even when additional clerical force must be employed. 


D/MCA/S/ONS or MAIN BUILDJNG-4JXU3’ 
' S WITCH ROOM - SOX<50 



-^---30 £JA-?CAS T OVERFLOW n 
Fig. 53. Double-Deck Turbine Plant 


In some states stations furnishing light or power to the public 
are required to make annual reports and the system of records, ac¬ 
counting, and form of report are all prescribed by the state. 

Switchboard records consist, in alternating stations, of daily 
readings of feeder, recording wattmeters, and total recording watt¬ 
meter, together with voltmeter and ammeter readings at intervals 















































































































POWER STATIONS 


83 


of about 15 minutes, in some cases, to check upon the average 
power factor and determine the general form of the load curve. 
For direct-current lighting systems, volt and ampere readings serve 
to give the true output of the stations, and curves are readily plotted 
from these readings. The voltage should be recorded for the bus 
bars as well as for the centers of distribution. 




Fig. 54. Space Occupied by Turbo-Alternator Compared with that of Generator and 
• Reciprocating Engine of Same Capacity 


Indicator diagrams should be taken from the engines at fre¬ 
quent intervals for the purpose of determining the operation of 
the valves. Engine-room records include labor; use of waste, oil, 
and supplies; as well as all repairs made on engines, dynamos and 
auxiliaries. 

Boiler-room records include labor and repairs, amount of coal 
used, which amount may be kept in detail if desirable, amount 



























































84 


POWER STATIONS 


of water used, together with steam-gauge record and periodical 
analysis of flue gases as a check on the methods of firing. 



Records- for the distributing system include labor and ma¬ 
terial used for the lines and substations. For multiple-wire systems, 
frequent readings of the current in the different feeders will serve as a 
check on the balance of the load. 




POWER STATIONS 


85 


The cost of generating power varies greatly with the rate at 
which it is produced as well as upon local conditions. Station- 
operating expenses include cost of fuel, water, waste, oil, etc., cost 
of repairs, labor, and superintendence. Fixed charges include 
insurance, taxes, interest on investment, depreciation, and general 
office expenses. Total, expenses divided by total kilowatt-hours gives 



Fig. 56. A Good Arrangement of Apparatus for Substation 

the cost of generation of a kilowatt-hour. The cost of distributing a 
kilowatt hour may be determined in a similar manner. The rate 
of depreciation of apparatus differs greatly with different machines, 
but the following figures may be taken as average values, these fig¬ 
ures representing percentage of first cost to be charged up each year: 

Fireproof buildings from 2 to 3 per cent. 

Frame buildings from 5 to 8 per cent. 

Dynamos from 2 to 4 per cent. 

Prime movers from 2 \ to 5 per cent. 

Boilers from 4 to 5 per cent. 

Overhead lines, best constructed, 5 to 10 per cent. 

More poorly constructed lines 20 to 30 per cent. 

Badly constructed lines 40 to 60 per cent. 

Underground conduits 2 per cent. 

Lead covered cables 2 per cent. 



















8G 


POWER STATIONS 


Methods of Charging for Power. There are four methods 
used for charging consumers for electrical energy, namely, the flat- 
rate, or contract, system, the meter system, the two-rate meter system, 
and a system by which each customer pays a fixed amount depending 
on the maximum demand and in addition pays at a reasonable rate for 
the power actually used. 

In the flat-rate system, each customer pays a certain amount a 
year for service, this amount being based on the estimated amount 
of power to be used. These rates vary, depending on the hours of 
the day during which the power is to be used, being greatest if the 
energy is to be used during peak hours. It is an unsatisfactory method 
for lighting service, as many customers are liable to take advantage 
of the company, burning more lights than contracted for and at 
different hours, while the honest customer must pay a higher rate 
than is reasonable in order to make the station operation profitable. 
This method serves much better when the power is used for driving 
motors, and is used largely for this class of service. 

The simple meter method of charging serves the purpose bet¬ 
ter for lighting, but the rate here is the same no matter what hour 
of the day the current is used. Obviously, since machinery is in¬ 
stalled to carry the peak of the load, any power used at this time 
tends to increase the capital outlay from the plant, and users should 
be required to pay more for the power at such times. The meter 
system is often employed with a sliding scale or rate, the rate charged 
per kw.-hour depending upon the amount of electrical energy used. 

The two-rate meter accomplishes this purpose to a certain 
extent. The meters are arranged so that they record at two rates, 
the higher rate being used during the hours of heavy load. 

There are several methods of carrying out the fourth scheme. 
In the Brighton System a fixed charge is made each month, de¬ 
pending on the maximum demand for power during the previous 
month, a regular schedule of such charges being made out, based 
on the cost of the plant. An integrating wattmeter is used to re¬ 
cord the energy consumed, while a so-called “demand meter” records 
the maximum rate of demand. 























































PART IT 


POWER TRANSMISSION 

INTRODUCTION 

The subject of electrical power transmission is a very broad 
one as it deals with the transmission and distribution of electrical 
energy, as generated by the dynamo or alternating-current generator, 
to the receivers. The receivers may be lamps, motors, electrolytic 
cells, etc. Electrical distribution of power is better than other 
systems on account of its superior flexibility, efficiency, and effective¬ 
ness; and we find it taking the place of other methods in all but a 
few applications. For some purposes the problem is comparatively 
simple, while for other purposes, such as supplying a large system 
of incandescent lamps scattered over a comparatively large area, 
it is quite complicated. As with other branches of electrical engineer¬ 
ing, it is only in recent years that any great advances have been 
made in methods for the transmission of electrical power, and while this 
advance has been, rapid, there is still a large field for development. 

In a study of this subject, the different methods employed 
and their application, the most efficient systems to be installed for 
given service, the preparation of conductors and the calculation 
of their size, together with the proper installation of the same, 
should be considered. 

CONDUCTORS 

Material. Power, in any appreciable amount, is transmitted 
electrically by the aid of metal wires, cables, tubes, or bars. The 
materials used are iron or steel, copper, and aluminum; of these 
three, the two latter are the most important, iron or steel being 
used to a considerable extent only in the construction of telephone 
and telegraph lines, and even here they are rapidly giving way to 
copper. Steel may be used in some special cases, such as extremely 
long Spans in overhead construction or for the working conductors 
for railway installations using a third rail. Phosphor bronze has 
a limited use on account of its mechanical strength. 


POWER TRANSMISSION 


2 


TABLE I 

Copper Wire Table 


DIMENSIONS 

RESISTANCE 


Diameter 

Area 

Ohms Per Foot 

A. W. G. 






or 






B. & S. 

Inches 

Circular 

Mils 

At 20° C. 

At 50° C. 

AC80° C. 

0000 

.460 

211,600 

.00004893 

.00005467 

.00006058 

000 

.4096 

167,800 

.00006170 

.00006893 

.00007640 

00 

.3648 

133,100 

.00007780 

.00008692 

.00009633 

0 

.3249 

105,500 

.00009811 

.0001096 

.0001215 

1 

.2893 

83,690 

.0001237 

.0001382 

.0001532 

2 

.2576 

66,370 

.0001560 

.0001743 

.0001932 

3 

.2294 

52,630 

.0001967 

.0002198 

.0002435 

4 

.2043 

41,740 

.0002480 

.0002771 

.0003071 

5 

. 1819 

33,100 

.0003128 

.0003495 

.0003873 

6 

.1620 

26,250 

.0003914 

.0004406 

.0004883 

7 

.1443 

20,820 

.0004973 

.0005556 

.0006158 

8 

.1285 

16,510 

.0006271 

.0007007 

.0007765 

9 

.1144 

13,090 

.0007908 

.0008835 

.0009791 

10 

.1019 

10,380 

.0009972 

.001114 

.001235 

11 

.09074 

8,234 

.001257 

.001405 

.001557 

12 

.08081 

6,530 

.001586 

.001771 

.001963 

13 

.07196 

5,178 

.001999 

.002234 

.002476 

14 

.06408 

4,107 

.002521 

.002817 

.003122 

15 

.05707 

3,257 

.003179 

.003552 

.003936 

16 . 

.05082 

2,583 

.004009 

.004479 

.004964 

17 

.04526 

2,048 

.005055 

.005648 

.006259 

18 

.04030 

1,624 

.006374 

.007122 

.007892 


Copper and aluminum are used in the commercially pure state 
and are selected on account of their conductivity and comparatively 
low cost. The use of aluminum is at present limited to long¬ 
distance transmission lines or to large bus bars, and is selected on 
account of its being much lighter than copper. It is not used for 
insulated conductors because of its comparatively large cross- 
section and consequent increase in amount of insulation necessary. 
Other metals may serve to conduct electricity but they are not 
applied to the general transmission of energy. 

Weight. The specific gravity of copper is 8.89. The value 
for aluminum is 2.7, showing that aluminum weighs .483 times as 
















POWER TRANSMISSION 


3 


much as copper for the same conductivity or resistance. It is this 
property which makes its use desirable in special cases. Iron, as 
used for conductors, has a specific gravity of 7.8. 

Mechanical Strength. Soft-drawn copper has a tensile strength 
of 25,000 to 35,000 pounds per square inch. Hard-drawn copper 
has a tensile strength of 50,000 to 70,000 pounds per square inch, 
depending on the size; the lower value corresponding to Nos. 0000 
and 000. 

Aluminum has a tensile strength of about 33,000 pounds per 
square inch for hard-drawn wire i inch in diameter. For trans¬ 
mission purposes aluminum is used in the form of cable. 

Resistance. The resistance of electrical conductors is ex¬ 
pressed by the formula 



where R is total resistance of the conductors considered; l is length 
of the conductors in the units chosen; A is area of the conductors 
in the units chosen; and / is a constant depending on the material 
used and on the units selected. 

For cylindrical conductors, l is usually expressed in feet and 
A in circular mils. By a circular mil is meant the area of a circle 
.001 inches in diameter. A square mil is the area of a square whose 
sides measure .001 inches and is equivalent to 1.27 circular mils. 
Cylindrical conductors are designated by gauge number or by their 
diameter. The Brown & Sharpe (B. & S.) or American wire gauge 
is used almost universally and the diameters corresponding to the 
different gauge numbers are given in Table L Wires above No. 
0000 are designated by their diameter or by their area in circular 
mils. 

A convenient way of determining the size of a conductor from 
its gauge number is to remember that a No. 10 wire has a diameter 
of nearly one-tenth of an inch and the cross-section is doubled for 
every three sizes larger—Nos. 7, 4, etc.—and one-half as great for 
every three sizes smaller—Nos. 13, 16, etc. 1,000 feet of No. 10 
copper wire has a resistance of 1 ohm and weighs 31.4 pounds. 

When / is expressed in terms of the mil foot, a wire 1 foot in 
length having a cross-section of 1 mil, its value for copper of a purity 


1 


POWER TRANSMISSION 


TABLE II 

Resistances of Pure Aluminum Wire 


A. W. G. 
or 

B. & S. 

Resistance at 75° F. 

Ohms per 

1,000 feet 

Ohms per mile 

0000 

.08177 

.43172 

000 

•.10310 

.54440 

00 

.13001 

.68645 

0 

.16385 

.86515 

1 

.20672 

1.09150 

2 

.26077 

1.37637 

3 

.32872 

1.7357 

4 

.41448 

2.1885 

5 

.52268 

2.7597 

6 

.65910 

3.4802 

7 

.83110 

4.3885 

8 

1.06802 

5.5355 

9 

1.32135 

6.9767 

10 

1.66667 

8.8000 

11 

2.1012 

11.0947 

12 

2.6497 

13.9900 

13 

3.3412 

17.642 

14 

4.3180 

22.800 

15 

5.1917 

27.462 

16 

6.6985 

35.368 

17 

8.4472 

44.602 

18 

10.6518 

56.242 


known as Matthiessen’s Standard, or copper of 100 per cent con¬ 
ductivity, is 9.586 at 0° C.* For 99.5 per cent pure aluminum its 
value is given as 15.2. Table II gives the resistance of aluminum 
wire. This shows that the conductivity of aluminum is about 63 
per cent of that of copper. The conductivity of iron wire is about 
] that of copper. 

Matthiessen’s standard is based on the resistance of copper 
supposed, by Matthiessen, to be pure. Since his experiments, im¬ 
provements in the refining of copper have made it possible to produce 
copper of a conductivity exceeding 100 per cent. Copper of a con¬ 
ductivity lower than 98 per cent is seldom used for power-transmis¬ 
sion purposes. 


♦The commercial values given for the mil foot vary from 10.7 to 11 ohms. 









POWER TRANSMISSION 


5 


TABLE III 

Temperature Coefficients for Copper 


Int. Temp, in 
Degrees C. 

Temp. Coefficient 
per Degree C. 

Int. Temp, in 
Degrees C. 

Temp. Coefficient 
per Degree C. 

0 

.0042 

26 

.003786 

1 

.004182 

27 

.003772 

2 

.004165 

28 

.003758 

3 

.004148 

29 

.003744 

4 

.004131 

30 

.003730 

5 

.004114 

31 

.003716 

6 

.004097 

32 

.003702 

7. 

.004080 

33 

.003689 

8 

.004063 

34 

.003675 

9 

.004047 

35 

.003662 

10 

.004031 

36 

.003648 

11 

.004015 

37 

.003635 

12 

.003999 

38 

.003622 

13 

.003983 

39 

.003609 

14 

.003967 

40 

.003596 

15 

.003951 

41 

.003583 

16 

.003936 

42 

.003570 

17 

.003920 

43 

.003557 

18 

.003905 

44 

.003545 

19 

.003890 

45 

.003532 

20 

.003875 

46 

.003520 

21 

.003860 

47 

.003508 

22 

.003845 

48 

.003495 

23 

.003830 

49 

.003483 

24 

.003815 

50 

.003471 

25 

.003801 




Temperature Coefficient. The specific resistance—resistance 
per mil foot—is given for copper as 9.586 at 0° C. Its resist¬ 
ance increases with the temperature according to the approximate 
formula 

R t — R 0 (1 + at) 

where R t is resistance at temperature t° C.; R 0 is resistance at 0°C.; 
and a is the temperature coefficient, equal to .0042 for copper, com¬ 
mercial value. 

The value of a for aluminum does not differ greatly from this. 
It is usually taken as .0039. 














6 


POWER TRANSMISSION 


TABLE IV 

Safe Carrying Capacity of Wires 


A. W. G. 

OR 

Rubber Insulation 

Other Insulations 

B. & S. 

Amperes 

Amperes 

18 

3 

5 

16 

6 

8 

14 

12 

16 

12 

17 

23 

10 

24 

32 

8 

33 

46 

6 

46 

65 

5 

54 

77 

4 

65 

92 

3 

76 

110 

2 

90 

131 

1 

107 

156 

0 

127 

185 

00 

150 

220 

000 

177 

262 

0000 

210 

312 

Circular Mils 



200,000 

200 

300 

300,000 

270 

400 

400,000 

330 

500 

500,000 

390 

590 

600,000 

450 

680 

700,000 

500 

760 

800,000 

550 

840 

900,000 

600 

920 

1 , 000,000 

650 

1,000 

1 , 100,000 

690 

1,080 

1 , 200,000 

730 

1,150 

1 , 300,000 

770 

1,220 

1 , 400,000 

810 

1,290 

1 , 500,000 

850 

1,360 

1 , 600,000 

890 

1,430 

1 , 700,000 

930 

1,490 

1 , 800,000 

970 

1,550 

1 , 900,000 

1,010 

1,610 

2 , 000,000 

1,050 

1,670 




















POWER TRANSMISSION 


7 


The temperature coefficient for copper at temperature other 
than 0°C. is given by the Standardization Report of the A. I. E. E. 
in Table III. Knowing the resistance of a coil of wire at, say 25° 
C. (R, 5 ),in order to find its resistance at a temperature rise of 10° 
above 25 we have the formula 

R_ 5+10 = R ro (1 + 0.003801 X 10) 

In order to find the temperature risein degree centigrade from an initial 
resistance R. at a temperature i° C. and a final resistance of R i+r , we 
may use the formula 

r= (238.1 l] 

when r= rise in degrees centigrade. 

Effects of Resistance. The effect of resistance in conductors 
is threefold. 

(1) There is a drop in voltage, determined from Ohm’s law, 

E 

I = —, or E =IR 
R 

(2) There is a loss of energy proportional to the resistance and the 

E 2 

square of the current flowing. Loss in watts = I 2 R = —— 

R 

(3) There is a heating of the conductors, due to the energy lost, and 
the amount of heating allowable depends on the material surrounding the 
conductors. The drop in voltage or the heating limit is usually more im¬ 
portant in the design of a transmission system than the loss of energy. 

Current=Carrying Capacity. The temperature of a conductor 
will rise until heat is lost at a rate equal to the rate it is generated, 
so that a conductor is capable of carrying only a certain current 
with a given allowable temperature rise. The limit of this rise in 
temperature is determined by fire risk or injury to insulation. A 
general rule is that the current density should not exceed 1,000 amperes 
per square inch of cross-section for copper conductors. This value is 
too low for small wire and too high for heavy conductors, and it is 
governed by the way in which the conductors are installed. This 
value serves for bus bars where the thickness of the copper used is 
limited to \ inch. Curves shown in Figs. 1 and 2 are applicable tc 
switchboard wiring, and Table IV gives the safe carrying capacity of 
conductors for inside wiring. Perrine, in Table V, shows the class of 
conductors to be used under various conditions. 



8 


POWER TRANSMISSION 


Insulation. Insulation, in the form of a covering, is required 
for electrical conductors in all cases with the exception of switch¬ 
board bus bars and connections and wires used on pole lines, and 



Fig. 1. Curves Showing Safe Carrying Capacity of Copper Wires 

even these are often insulated. It may serve merely to keep the 
wires from making contact, as is the case with cotton- or silk-covered 
wire. Again, the wire may be covered with a material having a high 
specific resistance but being weak mechanically, and this combined 




































































































































































































































































































































































































































































































































POWER TRANSMISSION 


9 


with a material serving to give the necessary strength to the insu¬ 
lation. For this purpose yarns are used as the mechanical support, 
and waxes and asphaltum serve for the insulation proper. 



Annunciator wire is covered with heavy cotton yarn saturated 
with paraffin. The so-called underwriter’s wire is insulated with 
cotton braid saturated with white paint. Asphaltum or mineral 
wax is used for insulating weatherproof wire. It may be applied in 





































































































































































































































































































































































































































10 


POWER TRANSMISSION 


TABLE V 

PART I 


Conductors for Various Conditions 


Reference 

No. 

Remarks 

Reference 

No. 

Remarks 

1 

Not allowed 

8 

In insulating tubes 

2 

Clear spaces 

9 

In wood moldings 

3 

Through trees 

10 

Without further precaution 

4 

On glass insulators 

11 

If necessary 

5 

On porcelain knobs 

12 

Below 350 volts 

6 

In porcelain cleats 

13 

Above 350 volts 

7 

In wood cleats 




PART II 

Class of Conductors for Various Positions 



r 

i 


Position 





Description j 

i 



Con¬ 

Rooms 


Under¬ 

of Conductor 

i 

/ 

Damp 

looms 

cealed 

con¬ 

f - u . 

ground 

1 Open air 

Dry rooms 

under 

floor 

taining 
gases or 

O O 

T3 

C ^ 

P ^ 

T3 

.2 

In 

con¬ 





or wall 

vapor 

p 

« 

duit 

Bare wire. 

( 2 “ 4 ) 

1 

i 

1 

1 

1 

1 

2-4 


l 3-1 / 



Underwriter’s insulation. 

1 

/ 2-5 or 6 \ 
11 13 “ 1 / 

i 

1 

1 

1 

1 

1 

Double weatherproof. 

{ 12 " 4 \ 
\l3 & 2-4 J 

/ 2-5 or 6 1 

j 13-1 ft 

/ 12 “4\ 
j i3-ir 

1 

1 

1 

1 

1 

Triple weatherproof. 

13-4 

f 13-5 or G\ 

j 12-41 

r 12-81 

f 12-41 

1 

1 

1 


l or 8 / 

1 13_1 / 

1 13-1/. 

1 13_1 / 



Plain rubber. 

( 13-4 1 

13-5 

| 12-51 

13-8 ' 

f 12-5/ 

11 

J 

2-5 


l 3-1 / 

1 13 ~ 4 / 

1 13_4 / 



Taped or braided rubber. . . . 

13-4 

13-5 

f 12-51 
1 13-4f 

13-8 

1 12_5 l 
1 13 “ 4 / 

11 

1 

2-5 

Taped or braided cored rub-1 

13-4 

13-5 or 9 

/ 12-51 

13-8 

/ 12-5\ 




ber. / 

i 13-4/ 

1 13-4/ 

11 

1 

2-5 

Gutta-percha, armored. 

1 

1 

1 

1 

1 

10 

11 

1 

1 

11 

Rubber, ’saded. 

10 

9 

1 

8 

1 

Paper, leaded .. 1 



Fiber, leaded. / 

Any insulation, leaded and 

10 

9 

1 

8 

1 

11 

1 

11 

asphalted. 

l'O 

9 

6 

8 

6 

11 

11 

10 

L 




several ways, the best insulation being made by covering the con¬ 
ductor with a single braiding laid over asphaltum and then passing 
the covered wire through the liquid insulation, at the same time 
applying two cotton braids, and finishing by an external application 




















































POWER TRANSMISSION 


11 


of asphaltum and polishing. The most complete insulation is made 
up of a material which gives the most perfect insulation and which 
is strong enough, mechanically, to withstand pressure and abrasion 
without additional support. 

Gutta-percha is used for submarine cables but India rubber 
is the insulating material most used for electrical conductors. Gutta¬ 
percha cannot be used when exposed to the air, as it deteriorates 
rapidly under such conditions. Rubber, when used, is vulcanized, 
and great care is necessary in the process. This vulcanized rubber 
is usually covered with braid having a polished asphaltum surface. 
The insulation of high-tension cables will be considered in the dis¬ 
cussion of “Underground Construction”. 

DISTRIBUTION SYSTEMS 

SINGLE CIRCUIT 

Distribution systems may be divided into series systems and 
parallel systems, or combinations such as series-parallel or parallel- 
series systems. Various translating devices may be connected in 
circuit, changing from one 
system to the other, and 
the parallel system may be 
divided into single- and 
multiple-circuit systems 
commonly known as two- 
wire and three- or five-wire 
systems. 

Series. Series systems are applied to series arc lighting, to 
series incandescent lighting, and to constant-current motors driving 
machinery or generators feeding secondary circuits. They serve 
for both alternating and direct currents. Fig. 3 shows the arrange¬ 
ment of units in this system. The current, generated by the dynamo 
D, passes from the positive brush A, in direct-current systems, 
through the units L in series to the negative brush B. For lighting 
purposes, this current has a constant value and special machines 
are used for its generation. The voltage at the generator depends 
on the voltage required by the units and on the number of units 
connected in service. As an example, the voltage allowed for a direct- 
current open-arc lamp and its connections may be taken as 50 volts. 



Fig. 3. Diagram of Series Distributing System 





12 


POWER TRANSMISSION 


If 40 lamps are burning, the potential generated will be 50 X 40= 2,000 
volts. The number of units is sometimes great enough to raise this 
potential to 6,000 volts; but by a special arrangement of the Brush 
arc machine, known as the multiple-circuit arc machine, the potential 


is so distributed that its 
maximum value on the line 
is but 2,000 volts, provided 
the lamps are equally dis¬ 
tributed; while the toeal 
electromotive force gener¬ 
ated is 6,000 volts when 
the machine is fully loaded. 



-X —X — 1 ■ X ' 

Fig. 4. Brush Multiple Circuit Arc Machine 
Connections 


The machine is supplied with three commutators and the 
lamps are connected as shown in Fig. 4, which also shows the distri¬ 
bution of potential. 

All calculations for series systems are simple. The drop in 

E 

voltage is obtained from Ohm’s law, 1= —. A wire smaller than 

No. 8 should never be used for line construction, as it would not 
bi strong enough mechanically, even though the drop in voltage 
with its use should be well within the limit. 

The current taken by arc lamps seldom exceeds 10 amperes. 
For series incandescent lighting, the current may be lower than 
this, having a value of from 2 to 4 amperes. Special devices are 
used to prevent the breaking of a single filament from putting 
out all of the lights in the system, and automatic short-circuiting 
devices are used with series arc lamps for accomplishing the same 
purpose. 

As an example of the calculation of series circuits, it is required 
to find the drop in voltage and loss of energy in a line four miles 
long and composed of No. 8 wire, when the current flowing in the 
line is 9.6 amperes. From Table I we have a resistance of .0007007 
ohm per foot for No. 8 wire at 50° C. This gives a resistance of 3.7 
ohms per mile, or a resistance of 14.8 ohms for the circuit. From 
Ohm’s law, the drop in voltage equals current times resistance, or 
equals 9.6X14.8=142 volts. The loss in energy equals the square 
of the current times the resistance, or equals 9.6 2 X14.8= 1,364 watts.' 
If the circuit contains 80 lamps, each taking 50 volts, the total voltage 















POWER TRANSMISSION 


13 


of the system is 4,142 volts, and the percentage drop in pressure is 

142 o , 

^=3.43 per cent 

Parallel. In the parallel, or “multiple-arc,” system of distri¬ 
bution, the lamps or motors are supplied with a constant potential, 
and the current supplied by the generators is the sum of the currents 
taken by each translating device. There are several methods of 
distribution applicable to this system, each one having some char¬ 
acteristic which makes its use desirable for certain installations. 
The usual arrangement is to run conductors, known as feeders, 
out from the station, and connected to these feeders are other con¬ 
ductors, known as mains, to 


rOi 

O 

O 

O 


which, in turn, the receivers 
or translating devices are 
connected. Fig. 5 is a dia¬ 
gram of such a “feeder and 
main” system. 

The feeders may be con¬ 
nected at the same ends of 
the mains, known as parallel 
feeding; or they may be con¬ 
nected at the opposite ends 
of the main, giving us the 
anti-parallel system of feed¬ 
ing. The mains may be of uni¬ 
form cross-section through¬ 
out, or they may change in size so as to keep the current density 
approximately constant. The above conditions give rise to four 
possible combinations, namely, 

Case (1) Cylindrical conductors, parallel feeding, Fig. 6. 

Case (2) Tapering conductors, parallel feeding, Fig. 7. 

Case (3) Cylindrical conductors, anti-parallel feeding, Fig. 8. 

Case (4) Tapering conductors, anti-parallel feeding, Fig. 9. 


FEEDERS 

0 
o 
o 

LO-J 

Fig. 5. Diagram of “Feeder and Main” System 


The regulation of the voltage of a system is of particular im¬ 
portance when incandescent lamps are supplied; and the calcula¬ 
tion of the drop in voltage to lamps connected to mains supplied 
with a constant potential should be considered. Without going into 
detail as to the methods of derivation, we have the following for- 










14 


POWER TRANSMISSION 


mulas which apply to the above combinations when the receivers are 
uniformly distributed and each taking the same amount of current, 

RTx 

Case (1) D=^j-{2l-x) 

Case (2) D=2RIx 
RTx 

Case (3) D=-j-(l-x) 


Case (4) D=0 

where D is the difference between potentials applied to different 
lamps; R is the resistance of conductors per unit length at feeding 
_ point. This will be a con- 

<21 


<X> <> 5 0 < > 


stant quantity for cylin¬ 
drical conductors, but will 
change for tapering conduc¬ 
tors, having its minimum 
value at the feeding point, 
and its maximum value at 
the end of the main. I is 
the current in the main at 
the feeding point, or point 
at which the feeders are 
connected to the mains. In 
Figs. 6, 7,8, and 9 the mains 
only are shown in detail. 
x is the distance from the 
feeding point to the partic¬ 
ular lamps at which the vol¬ 
tage is being considered; and 
l is the length of the main. 
For Cases(l) and (2), the maximum difference of potential is found 
where x= l, that is, at the lamps located at the end of the mains. 
For Case (3), the maximum difference of potential is found where 

x=^-, or at the lamp located at the middle point of the mains. 


Fig. 6. Parallel Feeding System. Cylindrical 
Conductors 


0 0 £ <> < > 

Fig. 7. Parallel Feeding System. Tapering 
Conductors 

p—" sggya, 

Fig. 8. Anti-Parallel System. Cylindrical 
Conductors 

p gMSSS, 


Fig. ? 


Anti-Parallel System. Tapering 
Conductors 


For Case (4), the potential on all of the lamps is the same, but 
the difference between the voltage on the feeders and the voltage 
on the lamps is equal to RIl. 













POWER TRANSMISSION 


15 


For unequal distribution of receivers and special feeding points, 
the drop in voltage can be calculated by the aid of Ohm’s law, but 
this calculation becomes quite complicated for extensive systems. 
It usually is sufficient to keep the maximum drop within the desired 
limits when designing electrical conductors for lighting, being care¬ 
ful not to exceed the safe carrying capacity of the wires. 

The drop in voltage on the feeders may be calculated directly 
from Ohm’s law when direct current is used, knowing the current 
flowing and the dimensions of the conductors used. 

Additional formulas are given in “Electric Wiring,” which 
will aid in determining the size of wire to be used for a given instal¬ 
lation. 

As examples of calculation we have the following: 

System consists of 20 lamps, each taking .5 amperes. /=80 
feet. R= .01 ohm per foot at feeding point. Find the maximum 
difference of potential on the lamps in each of the first three cases. 

I = 20 X .5 = 10 amperes 

Case (1) D = ' 01 X c , 1 n °* -° X(160 - 80) = 8 volts 

Case (2) 

Case (3) 

In Case (4), the difference in potential applied to the lamps and 
the potential of the feeders would be .01X10X80=8 volts. 

Again, with the maximum allowable drop given, the resistance 
of the wires at the feeding point may be determined. For taper¬ 
ing conductors, the current density is kept approximately con¬ 
stant by using wire of a smaller diameter as the current decreases. 
Thus supposing, as in the case considered, that the resistance at 
the feeding point was .01 ohm per foot. At a distance of 40 feet 
from the feeding point the current would be only J of 10, or 5 am¬ 
peres, and the size of the wire would be one-half as great, giving it a 
resistance at this point of .02 ohm per foot. 

Feeding Point. In order to determine the point at which a 
system of mains should preferably be fed, that is, the point where 


D =2 X .01 X 10 X 80 = 16 volts 


80 

.01X 10 X — 

Z) =-- x 

80 


^80 — ^ ) = 2 volts 




16 


POWER TRANSMISSION 


the feeders are attached to the mains, it is necessary to find the 
electrical center of gravity of the system. The method employed 
is similar to that used in determining the best location of a power 
plant as regards amount of copper required, and consists of sepa¬ 
rately obtaining the center of gravity of straight sections and then 
determining the total resultant and point of application of this 
resultant of the straight sections to locate the best point for feed¬ 
ing. Actual conditions are often such that the system cannot be 



Fig. 10. Diagram to Determine Feeding Point 


fed at a point so determined, but it is well to run the feeders as 
close to this point as is practical, as less copper is then required for 
a given drop in potential. 

Consider, as an example, a system such as is shown in Fig. 10. 
The number of lamps and location of the same are shown in this 
figure. The loads A, B, C, D, may be considered as concentrated 
at A' } a point 33.8 feet from / and equal to A + B + C + D. This 
point is obtained as follows: 















































POWER TRANSMISSION 


17 


Ax— By \0y=20x .r + ?/=400 

A + B =30 x= 133.3 feet. 

Cx'=Dy' 15*'= 2 Oy’ *'+!/'=.500 *'=285.7 feet. 

C+D= 35 

(A + B)x"= (C+D)y" x"+y"=6S2A 

30*"= 35 y" *"=340.5 feet. 

A-^-B-\-C-\-D= 65 

A' is 6.2 feet from C or 33.8 feet from 7. 

E and F may be combined to form a group of 30 lamps and 
the resultant of E, F, G, and 77 is 70 lamps located at B', a point 
310 feet from J, this point being located in the same manner as 
A'. Similarly, we find the resultant of the loads at A' and B' to 
be 135 lamps located at C', a point 331.1 feet from 7, and the proper 
feeding point for the system. 

A'= 65 lights, 33.8 feet from 1 
B' = 70 lights, 310 feet from J 
Distance IJ= 360 feet 

Distance from A f to B'= 360 + 310 + 33.8= 703.8 feet 

65z=70 y 

x-\-y— 703.8 feet 

x= 364.9 feet 

364.9—33.8=331.1 feet 

Feeding at a point 331.1 feet from I, the main should be connected 
to the point A in order for the potential drop from the feeding point 
to be the same to the points A, D, and II, and 33.8 feet of extra main 
would be required. If no change in the mains is to be made, then 
the system may be resolved into a linear system by starting at the 
branch on which the drop of potential will be a maximum, the branch 
leading to I) in the above problem, and considering the other branches 
as if they were concentrated loads applied at the points where the 
branches are taken off. Thus, loads A and B are added and con¬ 
sidered as a load of 30 amperes applied at 7, and loads E and F 
are combined and considered as a load of 30 amperes applied at a 
point 350 feet from 7. We then have a linear system consisting 
of loads as follows: 20 amperes at the end D, 15 amperes 500 feet 
from D at C, 30 amperes 540 feet from D at 7, 30 amperes 890 feet 


18 


POWER TRANSMISSION 


from D, 25 amperes 1,300 feet from D at G, and 15 amperes 1,700 
feet from D at H. The feeding point is then found from the equation 
giving the distance to the center of gravity (uniform size or conductor 
assumed): 


Distance from D to best 
feeding point in feet 


20X0 + 15X500 + 30X540 + 30X890 
+ 25X1300 + 15X1700 

20+15 + 30 + 30 + 25 + 15 
108400 


135 


= 803 


Distance from 7 to best feeding point = 803—540 = 263 feet. 

The above is a simple definite case. Should the load be variable, 
the proper feeding point will change with the load, and, in extensive 
systems, the location of this point can be obtained approximately 
only. The same method of calculation is employed in locating the 
points from which sub-feeders are run out from the terminals of the 
main feeders as is the case in large systems, the voltage being main¬ 
tained constant at the point where the sub-feeders are connected 
to the feeders. 

Good practice shows the drop in potential to be within the 
following limits: 


From feeding points (points where sub-feeders or mains 


are attached) to lamps. 5 per cent 

Loss in sub-feeders. 3 per cent 

Loss in mains. 1.5 per cent 

Loss in service wires. 0.5 per cent 


The actual variation of voltage should not exceed 3 per cent. 

Series-Multiple and Multiple-Series. In the series-multiple 
and the multiple-series systems, groups of units, connected in mul¬ 
tiple, are arranged in series in the circuit, or groups of units are con¬ 
nected in series and those, in turn, connected in multiple, re¬ 
spectively. The application of such systems is limited. They are 
used to some extent in street-lighting when incandescent lamps 
are used. 

MULTIPLE CIRCUIT 

Three-Wire. We have seen that in any system of conductors 
the power lost is equal to I 2 R. For a given amount of power trans¬ 
mitted, IE, the current varies inversely with the voltage and con- 








POWER TRANSMISSION 


19 



Fig. 11. Diagram of 3-Wire Lighting System 


sequently the amount of power lost, which is directly proportional 
to the square of the current, is inversely proportional to the square 
of the voltage. Hence, for the same loss of power and the same 
percentage drop in voltage, doubling the voltage of the system would 
allow the resistance of the conductors to be made four times as great, 
and wire of one-fourth the cross-section or one-fourth the amount 
of copper would be required. 

The voltage for which incan- 
descent lamps, having a rea- 
sonable efficiency, can be eco¬ 
nomically manufactured is lim¬ 
ited to 220, while the majority 
of them are made for 110. In order to increase the voltage on the 
system, a special connection of such lamps is necessary. The three- 
wire and five-wire systems are adopted for the purpose of increasing 
this voltage. Fig. 11 shows a diagram of a three-wire system. 
Consider the conductor B removed and we have a series-multiple 
system with two lamps in series.' This arrangement does not give 
independent control of individual lamps, and the third wire is in¬ 
troduced to take care of any unbalancing of the number of lamps 
or units connected on either 
side of the system, and to al- 
low more freedom in the loca- 

tion of the lights. The cur- (j)/ (J)/ (j)/ (J)/ (Jy 

rent flowing in the conductor “ — e 
B, known as the neutral con- Fig - 12 - 
ductor, depends on the differ¬ 
ence of the currents required by the units on the two sides of the * 
system. Fig. 12 shows a system in which the loads on the two sides 
are unequal, an unbalanced system, with the value of the current 
in the neutral wire at different points. Each unit is here assumed 
to take one ampere. 

As stated above, were no neutral wire required, the amount 
of copper necessary for a system with the lamps connected, two in 
series, for the same percentage drop in voltage would be one-fourth 
the amount necessary for the parallel connection. This may be 
shown as follows: The current in the wire in the first case is one- 
half as great, so that the voltage drop would be divided by two for 


^ —4 


£ 


B 


Diaeram of 3-Wire System— 
Unbalanced Load 









20 


POWER TRANSMISSION 


the same size wire. The voltage on the system is twice as great, 
so that, with the same percentage regulation, the actual voltage 
drop would be doubled. Consequently wire of one-fourth the cross- 
section and weight may be used. If the neutral wire is made one- 
half the size of the outside conductor, as is usually the case in feed¬ 
ers, the amount of copper required is A of that necessary for the 
two-wire system. For mains it is customary to make all three con¬ 
ductors the same size, increasing the amount of copper to f of that 
required for a two-wire system. For a five-wire system with all 
conductors the same size, the weight of copper necessary is .156 
times that for a two-wire system. 



Fig. 13. Diagrams of 3-Wire Generating Methods 


Multiple-wire systems have no advantage other than a saving 
of copper, except when used for multiple-voltage systems, while 
among their disadvantages may be mentioned: 

Complication of generating apparatus 
Complication of instruments and wiring 
Liability to variation in voltage, due to unbalancing of load 





























POWER TRANSMISSION 


21 


Generating Methods. Fig. 13 shows some of the methods employed 
in generating current for a three-wire system. 

(A) Two dynamos connected in series. 

(B) A double dynamo. 

(C) Bridge arrangement, using a resistance with the neutral connec¬ 
tion arranged so as to change the value of resistance in either side of the sys¬ 
tem. Has the disadvantage of continuous loss of energy in the resistance. 

(D) Storage battery connected across the line with neutral connected 
at middle point. 

(E) Special dynamo supplied with three brushes. 

(F) Special machine having collector rings, across which is connected 
an impedance coil, the neutral wire being connected to the middle point of 
this coil. 

(G) Compensators or motor-generator set used in connection with gen¬ 
erator. The motor-generator set is known as a balancer set. 

Storage batteries are not installed primarily for furnishing volt¬ 
age for a three-wire system, but when installed primarily for other 
purposes, they may be used for the three-wire distribution. 

Another type of three-wire dynamo is equipped with balancing 
coils placed on the armature and a collector ring and neutral brush 
added, thus doing away with the reactance coil of F but adding to 
the armature winding. 

Three-wire dynamos or compensators are at present used in 
preference to the other systems illustrated. 

Compensators are usually wound for about 10 per cent of the 
capacity of the machine with which they are used. A 10-kilowatt 
balancer set will take care of a load on the neutral, which, at the 
voltage of one side of the system, would give a total of 10 kilowatts. 
In the motor-generator set, one side becomes a motor or generator 
depending on whether the load on that side is less or greater than the 
load on the opposite side. 

Voltage Regulation. It is customary to keep the voltage on 
the mains constant, or as nearly so as possible, at the point where 
the feeders are attached. Where but one set of feeders is run out 
from the station, this may readily be accomplished by the use of 
over-compounded dynamos, adjusted to give an increase of voltage 
equal to the drop in the feeders at different loads. Again, the field 
of a shunt-wound generator may be controlled by hand, the pres¬ 
sure at the feeding points being indicated by a voltmeter connected 
to pilot wires running from the feeding point back to the station. 


22 


POWER TRANSMISSION 


When the system is more extensive, separate regulation of 
different feeders is necessary. A variable resistance may be placed 
in series with separate feeders, but this is undesirable on account 
of a constant loss of energy. Feeders may be connected in along 
a system of mains and one or more of these switched in or out of 
service as the load changes. Bus bars giving different voltages 
may be arranged so that the feeders can be changed to a higher 
voltage bar as the load increases. Boosters—series dynamos may 
be connected in series with separate feeders and these may be ar¬ 
ranged to regulate the voltage automatically. The use of boosters 
is not to be recommended except for a few very long feeders, and 
then the total capacity of boosters should equal but a small per¬ 
centage of the station output if the efficiency of the system as a 



whole is to remain high. Fig. 14 is a diagram of a system using 
different methods of voltage regulation. 

ALTERNATING CURRENT 

Alternating-current systems of distribution may be classified 
in a manner similar to direct-current systems, that is, as series and 
parallel systems; but in addition to these we have a classification 
depending on the number of phases used, such as single-phase, 
quarter- or two-phase, and three-phase systems. 

Series. The series system may consist of a simple series circuit 
fed by a constant-current generator, or it may be fed by a constant- 
current transformer, the primary of which is supplied with a con¬ 
stant potential, the secondary furnishing a constant current. For 























POWER TRANSMISSION 


23 


a description of such a transformer, see “Electric Lighting”. Again, 
the current may be maintained constantly by means of a constant- 
current regulator, such as is described in “Electric Lighting”. Con¬ 
stant-current alternators are seldom used, the two latter forms of 
regulation being applied to most series installations. The prin¬ 
cipal application of series alternating-current systems is to street¬ 
lighting. Parallel-series alternating-current systems are sometimes 
used for street-lighting with incandescent lamps. 

Parallel. Parallel systems using alternating current are also 
analogous to parallel systems using direct current, though the re¬ 
ceivers, especially if lamps, are seldom connected directly to the leads 
coming from the station, but are fed from the secondaries of constant- 
potential transformers, which are connected to the lines in parallel, 
and step down the voltage. The 
readiness with which the voltage 
of such systems may be changed 
by means of suitable transform¬ 
ers is the chief advantage of the 
single-phase systems. The volt¬ 
age may be generated at, or 
transformed up to, a high value 
at the station, transmitted a 
considerable distance over small 
conductors with little loss of 
energy, and then transformed to 
the desired value for the con¬ 
nected units. Transformers may readily be constructed to furnish 
voltage for a three-wire secondary distribution. Fig. 15 is a diagram 
of a single-phase system supplying power to both tw T o-wire and 
three-wire systems. Two separate transformers are used for ob¬ 
taining the three-wire system, in one case, and a transformer, sup¬ 
plied with a tap connected to the middle point of the secondary, 
is used in the other case. 

Voltage Regulation. The regulation of voltage for alternating- 
current systems may be accomplished, as in direct-current installa¬ 
tions, by means of compounding (“composite-wound alternators”), 
hand regulation, or resistance or reactance connected in series with 
the feeders. In addition, the feeders may be controlled by means 


rO-i 

-o- 

-o- 



Fig. 15. Single-Phase System with Secondary 
3-Wire System 
























24 


POWER TRANSMISSION 


of special regulators, such as the Stillwell regulator, or the “C R” 
regulator, which consist of transformers with the primary coil con¬ 
nected across the line and the secondary in series with the line, and 
so arranged that the number of turns in one or both windings may 
be varied; other forms of regulators are the magnetic regulator and 
the induction regulator. 

For the automatic control of generator voltage, the composite- 
wound alternator has been discarded and the Tirrill regulator sub- 



Fig. 16. Tirrill Regulator for Operating Directly on Generator Field 

stituted. The Tirrill regulator is used for the voltage control of 
either direct- or alternating-current machines and maintains a steady 
potential at the bus bars, irrespective of the nature or the amount 
of the load. In the case of either the alternating-current system 
or the direct-current machines, the regulator may be adjusted so 
as to automatically raise the bus-bar potential as the load is in¬ 
creased, thus holding a steady voltage at some point out on the 
line; or it may be used to hold the voltage steady at the bus bars. 


















POWER TRANSMISSION 


25 


For small direct-current machines, the regulator operates directly 
upon the field of the generator, but for larger machines of the direct- 
current type or for alternators the regulator acts upon the field of a 
separate exciter. The general appearance of the Tirrill regulator 
for operating directly on the shunt field of a dynamo is shown in 
Fig. 1G, and the diagram for the elementary connections is shown 
in Fig. 17. Referring to Fig. 17, the operation may be explained 
as follows: The field rheostat is adjusted until the generator 
gives about 65 per cent of normal potential on open circuit, in 
which case, when the regulator is put into operation, the potential 
winding of the main control magnet is excited below normal, and 
the main contacts are closed. With the main contacts closed, 
both windings of the relay magnet are excited and the relay contacts 
are closed on account of the fact that the relay magnet is differentially 


COMPELS A T/NG 



wound. When the. relay contacts are closed, the field rheostat is 
cut out of circuit and the generator voltage builds up. Any tendency 
to go above the voltage for which the regulator is adjusted allows 
the main contacts and the relay contacts to open, thus inserting the 
field resistance. In operation the main and relay contacts are in a 
continuous state of vibration and a steady voltage is maintained at 
the bus bars. In case the compensating winding is used, a steady 
voltage is maintained at the bus bars, but its value will be deter¬ 
mined by the adjustment of the compensating winding and the 
value of the load. 


































26 


POWER TRANSMISSION 


A regulator designed to operate on the field of a separate exciter 
is shown in Fig. 18, and its operation may be explained by reference 
to Fig. 19. The field rheostat of the exciter is adjusted until 
the alternator gives 65 per cent of its normal voltage on open circuit. 



Fig. 18. Form of Tirrill Regulator Operating on Field of Exciter 

The direct-current control magnet and the potential winding of the 
magnet connected to the secondary of the potential transformer 
are both under-excited and the floating main contacts are closed. 
















POWER TRANSMISSION 


27 


This closes the circuit through the second winding of the relay mag¬ 
net and the relay contacts are closed, thus short-circuiting the field 
rheostat in the exciter field and raising the potential of the exciter 
and the alternator. The contacts are in constant vibration and a 
steady and constant potential is maintained at the bus bars in case 
the compensating winding is not in use. When the compensating 
winding is connected -in, the potential at the bus bars remains 
steady but its value depends upon the adjustment of the regulator 
and the value of the load. The condenser shown in these diagrams 
is for the purpose of preventing excessive sparking at the contacts. 

Polyphase. Polyphase systems of distribution are used where 
motors are to be run from the circuits; also for long-distance trans¬ 
mission lines, partly on account of the saving in copper. Polyphase 



generators may be constructed more cheaply, for a given output, 
than single-phase machines because of a better utilization of the 
winding space on the armature; while single-phase motors, except 
in small sizes, or series motors as applied to railway work, are not 
entirely satisfactory. The large majority of machines installed at 
the present time for either power or lighting are of the polyphase 
type. Two-phase and three-phase systems are the only ones that 
are in common use for power transmission, three phases being used 
for long-distance transmission lines. Six phases are used for rotary 
converters only, the capacity of the machines being greatly increased 
when connected six-phase. 









































28 


POWER TRANSMISSION 


Amount of Copper for Different Systems. The amount of copper 
required for the different systems, assuming the weight of copper for 
a single-phase two-wire system to be 100 per cent, is as follows: 

Single-phase two-wire systems..100 per cent 

Single-phase three-wire systems (Neutral wire same 

size as outside wires). 37.5 per cent 

Two-phase four-wire system.100 per cent 

Two-phase three-wire system. 72.9 per cent 

Three-phase three-wire system. 75 per cent 

Three-phase four-wire system.33.3 per cent 

----— This assumes the voltage on 

L__ the receivers to be the same in 

every case, the maximum volt¬ 
age having different values, de¬ 
pending on the- system used. 
The three-phase three-wire sys¬ 
tem is preferable to the two- 
phase three-wire system for 
most purposes on account of 
better voltage regulation. In 
the three-phase four-wire sys¬ 
tem the maximum voltage is 
V 3 times the voltage on the 
receivers. Were the same 
maximum voltage allowable as 
in the three-phase three-wire 
system, the amount of copper 
for the three-phase four-wire 

system would be | that required 
for the three-phase three-wire 
system. Fig. 20 shows, dia- 

grammaticallv, the connections of the different systems. In the 
•three-phase four-wire system, single-phase loads are connected 

between the outside wires and the neutral, the neutral being the 

conductor leading to the common connection of the three phases. 

As an example of the way in which the relative amounts of 
copper are calculated, take the three-phase three-wire system. 
Assume the amount of power transmitted to be P and the percent¬ 
age loss of energy to be p. Let E be the voltage on the receiver, 




Fig. 20. Diagrams of Principal 
Wiring Systems 











































POWER TRANSMISSION 


29 


I be the current flowing in a single conductor, single-phase system, 
and V be the current in a single conductor, three-phase system. We 
have for the single-phase two-wire system 


P=IE 


and for the three-phase three-wire system 

P = V'V I’E 
> IE = v'V I'E 

7' = —L= 

V 3 

The loss in energy in the two-wire system=pP= 2 7 2 R, when 
R is the resistance of one conductor. The loss in energy in the 
three-phase system = pP= 3 P 2 R r , when R' is the resistance of a sin¬ 
gle conductor in the three-phase system. 

Substituting ~^= for we have 


V 3 


2 PR= 


3 PR' 

~3~‘ 


or 2 R= R' 


The amount of copper is inversely proportional to the resist¬ 
ance of the conductor, so that if W is 'the weight of one conductor 
for a single-phase system and W is the weight of one conductor for 
a three-phase system 

W—2 W 


Two conductors are required in the first case =2 W. 
Three conductors are required in the second case=3 W'. 

3 W'— | W 

2 W = 2 W 

3 W' I W 

2W = ^-. = i = 75per cent 

TRANSMISSION LINES 


Capacity. Conductors, used for the transmission of power, 
together with their metallic shields, the ground, and neighboring 
conductors, form condensers, which, when the line is long, have 
an appreciable capacity. The capacity of circuits is quite readily 
calculated, the following formula applying to individual cases. 




30 


POWER TRANSMISSION 


Case (1)—Insulated cable with lead sheath. 

38.83 k 10 


C— 


log 


per mile 


Case (2)—Single conductor with earth return. 

~ 38.83 X lO" 3 

' ih —- p er mile 

log T 


Case (3)—Parallel conductors forming a metallic circuit. 

~ 19.42 X 10“ 3 « . . 

C= -—-per mde ot circuit 

i 2^1 

log T 

where C is capacity in microfarads; k is specific inductive capacity 
of insulating material; 1 for air; 2.25 to 3.7 for rubber; D is inside 
diameter of lead sheath; d is diameter of conductor; h is distance 
of conductors above ground; and A is distance between wires. 

Common logarithms apply to these formulas and for a metallic 
circuit, C is the capacity between wires. 

If the capacity be taken between one wire and the neutral point 
of a system, or the point of zero potential, the capacity is given as 


C (in microfarads) = 


.0776 


2 log 


2A 


per 


mile of circuit * 


Table VI gives the capacity, to the neutral point, of different 
size wire used for three-phase transmission lines. 

The effect of this capacity is to cause a charging current, 90 
degrees in advance of the impressed pressure, to flow in the circuit, 
and the regulation of the system is affected by this charging current 
as will be seen later. Capacity may be reduced by increasing the 
distance between conductors or in lead-sheathed cables, by using 
insulation of low specific inductive capacity, such as paper. 

Inductance. Self-Inductance. The self-inductance of lines is 
very readily calculated. The following formula is apphcable to 

*A mile of circuit includes two miles of conductor in a single-phase system and three 
miles of conductor in a three-phase system. 







POWER TRANSMISSION 


31 


TABLE VI 

Capacity in Microfarads per Mile of Circuit for Three=Phase System 


Size 

B. & S. - 

Diameter 

in 

Inches 

Distance 

in 

Inches 

Capacity 

C in 
Micro¬ 
farads 

Size 

B. & S. 

Diameter 

in 

Inches 

Distance 

in 

Inches 

Capacity 
C in 
Micro¬ 
farads 

0000 

.46 

12 

.0226 

4 

.204 

12 

.01874 



18 

.0204 



18 

.01726 



24 

.01922 



24 

.01636 



48 

.01674 



48 

.01452 

000 

.41 

12 

.0218 

5 

.182 

12 

.01830 



18 

.01992 



18 

.01690 



24 

.01876 



24 

.01602 



48 

.01638 



48 

.01426 

00 

.365 

12 

.0124 

6 

.162 

12 

.01788 



18 

.01946 



18 

.01654 



24 

.01832 



24 

.01560 



48 

.01604 



48 

.0140 

0 

.325 

12 

.02078 

7 

.144 

12 

.01746 



18 

.01898 



18 

.01618 



24 

.01642 



24 

.01538 



48 

.01570 



48 

.01374 

1 

.289 

12 

.02022 

8 

.128 

12 

.01708 



18 

.01952 



18 

.01586 



24 

.01748 



24 

.01508 



48 

.0154 



48 

.01350 

2 

.258 

12 

.01972 

9 

.114 

12 

.01660 



• 18 

.01818 



18 

.01552 



24 

.01710 



24 

.01478 



48 

.01510 



48 

.01326 

3 

.229 

12 

.01938 

10 

.102 

12 

.01636 



18 

.01766 



18 

.01522 



24 

.01672 



24 

.01452 



48 

.01480 



48 

.01304 


copper or aluminum conductors, three-phase system; per mile of 
circuit. 

L= .000558 [2.303 log^) + .25] 

where L is inductance of the loop of a three-phase circuit in henrys. 






















32 


POWER TRANSMISSION 


TABLE VII 

Inductance per Mile of Three=Phase Circuit 


Size 

B. & S. 

Diameter 

in 

Inches 

Distance 

in 

Inches 

Self-in¬ 
ductance 
L Henrys 

Size 

B. & S. 

Diameter 

IN 

Inches 

Distance 

in 

Inches 

Self-in¬ 

ductance 

L Henrys 

0000 

.46 

12 

.00234 

4 

.204 

12 

.00280 



18 

.00256 



18 

.00300 



24 

.00270 



24 

.00315 



48 

.00312 



48 

.00358 

000 

.41 

12 

.00241 

5 

.182 

12 

.00286 



18 

.00262 



18 

.00307 



24 

.00277 



24 

.00323 

V 


48 

.00318 



48 

.00356 

00 

.365 

12 

.00248 

6 

.162 

12 

.00291 



18 

.00269 



18 

.00313 



24 

.00285 



24 

.00329 



48 

.00330 



48 

.00369 

0 

.325 

12 

.00254 

7 

.144 

12 

.00298 



18 

.00276 



18 

.00310 



24 

.00293 



24 

.00336 



48 

.00331 



48 

.00377 

1 

.289 

12 

.00260 

8 

.128 

12 

.00303 



18 

.00281 



18 

.00325 



24 

.00308 



24 

.00341 



43 

.00338 



48 

.00384 

2 

.258 

12 

.00267 

9 

.114 

12 

.00310 



18 

.00288 



18 

.00332 



24 

.00304 



24 

.00348 


• 

48 

.00314 



48 

.00389 

3 

.229 

12 

.00274 

10 

.102 

12 

.00318 



18 

.00294 



18 

.00340 



24 

.00310 



24 

.00355 



48 

.00351 



48 

.00396 


In Tables VI and VII a mile of circuit refers to one mile of pole line. 


For a single-phase line the inductance of a loop for a mile of 
line or circuit, two miles of wire, the formula is 


Z=.000644 






















POWER TRANSMISSION 


33 


Where we use the “inductance of one wire” we have 
L= .000322 [2.303 log 2 -j + . 25 ] 

Table VII is based on the above formula for a three-phase 

line. 

Self-inductance is reduced by decreasing the distance between 
wires and it disappears entirely in concentric conductors. Sub¬ 
dividing the conductors decreases the drop in voltage due to self¬ 
inductance but it complicates the wiring. Circuits formed of con¬ 
ductors twisted together have very little inductance. When alter¬ 
nating-current wires are run in iron pipes, both wires of the circuit 
must be run in the same pipe, inasmuch as the self-inductance 
depends on the number of magnetic lines of force passing between 
the conductors or threading the circuit, and this number will be 
increased when iron is present between the conductors. 

The effect of self-inductance in a circuit is to cause the cur¬ 
rent to lag behind the impressed voltage and it also increases the 
impedance of the circuit. 

The effect of self-inductance may be neutralized by capacity 
or vice-versd. The relative value of the two for complete neutraliza- 
tion must be 

c= 1 

I (2 

where C and L are in farads and henrys, respectively, and i is the 
frequency of the system. d 

Mutual-Inductance. By mutual-induc¬ 
tance is meant the inductive effect one cir¬ 
cuit has on another separate circuit, gener¬ 
ally a parallel circuit in power transmission. 

An alternating current flowing in one circuit 
sets up an electromotive force in a parallel 
circuit which is opposite in direction to the 
e. m. f. impressed on the first circuit, and 
is proportional to the number of the lines 
of force set up by the first circuit which thread the second circuit. 

The effects of mutual-inductance may be reduced by increasing 
the distance between the circuits, the distance between wires of 


•A 


•C 


•D 


•B 


Fi<z. 21. Section of Conduc¬ 
tors Arranged to Reduce 
Mutual Inductance 



34 


POWER TRANSMISSION 


a circuit remaining the same. This is impractical beyond a certain 
extent, if the circuits are to be run on the same pole line, so that a 
special arrangement of the conductors is necessary. 

Figs. 21 and 22 show such special arrangements. In Fig. 21 
AB forms the wires of one circuit and CD the wires of the other 
circuit. Lines of force set up by the circuit A B do not thread the 
circuit CD, provided A, B, C, and D are arranged at the corners of 
a square so that there is no effect on the circuit CD. In Fig. 22 
assume an e. m. f. to be set up in the portion of the circuit CD in 
the direction of the arrows. The e. m. f. in the section DE will 


A 


B 



Fig. 22. Transposition Diagram of Ten Two-Wire Circuits to Reduce Mutual-Inductance 

then be in the direction of the arrows shown and the effects on the 
circuit AB will be neutralized, provided the transposition, as the 
crossing of the conductors is called, is made at the middle of the 
line. Such transpositions are made at frequent intervals on trans¬ 
mission lines in order to do away with the effects of mutual-inductance 
which, at times, might be considerable. When several circuits 
are run on the same pole line, these transpositions must be made 
in such a manner that each circuit is transposed in its relation to 





















































































POWER TRANSMISSION 


35 


the other circuits. The transposition of the circuits of a line com¬ 
posed of ten two-wire circuits is shown in Fig. 22. 

In the three-phase circuits, it is customary to transpose the three 
wires in order to do away with the effects of mutual-induction 



5 

e 

J 


Fig. 23. Transposition Diagram of Three Parallel Three-Phase Lines 
to Reduce Mutual-Inductance 

and in these transpositions the relative location of the wires is changed 
so as to bring each conductor the same average distance from every 
other parallel conductor. Fig. 23 shows the way in which the con¬ 
ductors of three parallel three-phase lines may be transposed so as 
to do away with disturbances due to mutual induction. The length 
of the straight section varies in practice from about one-half mile 
to five miles. 

ALTERNATING=CURRENT LINES 

Calculations. In dealing with alternating currents, Ohm’s 
law can be applied only when all of the effects of inductance and 
capacity have been eliminated and, since this can seldom be accom¬ 
plished, a new formula must be used which takes such capacity and 
inductance effects into account. Not only the inductance or capacity 
of the line itself must be considered, but the nature of the receiver 
must be taken into account as well, when the regulation of the system 
as a whole is being considered. The following quantities must be 
known in the complete solution of problems relating to alternating- 
current systems: 

(1) Frequency of the current used; 

(2) Self-induction and capacity of the receivers; 

(3) Self-induction and capacity of the lines; 

(4) Voltage of, and current flowing in, the lines; 

(5) Resistance of the various parts. 














36 


POWER TRANSMISSION 


General Wiring Formulas. The following set of formulas, 
together with Table VIII, are used for calculating transmission lines 
proper when using direct or alternating current and for frequencies 
varying from 25 to 125, and for single and polyphase currents. 


Area of conductor, circular mils= 


D X W X C' 
pXE 2 


Current in main conductors = 


WXT 

E 


where IF is total watts delivered; D is distance of transmission (one 
way) in feet; p is loss in line in per cent of power delivered, that is, 
of W; and E is voltage between main conductors at receiving or con¬ 
sumer’s end of circuit. 

For continuous current C' =2,160, T= 1 , B= 1 , and 4 = 6.04. 


Volts loss in lines = 


pXEXB 


Pounds copper = 


100 

D 2 X WX C'XA 
pXE 2 X 1,000,000 


The following formula will be found convenient for calculating 
the copper required for long-distance three-phase transmission 
circuits: 

„ , M 2 X kw.X 300,000,000 

Pounds copper = - ^ X E 2 - 

where M is the distance of transmission in miles; kw. is the power 
delivered in kilowatts; and the power factor is assumed to be ap¬ 
proximately 95 per cent. 


Application of Formulas. The value of C' for any particular power 
factor is obtained by dividing 2,160—the value for continuous current—by 
the square of that power factor for single-phase, by twice the square of that 
power factor for three-wire three-phase, or four-wire two-phase. 

The value of B depends on the size of wire, frequency, and power factor. 
It is equal to 1 for continuous current, and for alternating current with 100 
per cent power factor and sizes of wire given in Table VIII. 

Note —The figures given are for wires 18 inches apart, and are sufficiently 
accurate for all practical purposes provided the displacement in phase betwe< n 
current and e.m.f. at the receiving end is not very much greater than that 
at the generator; in other words, provided that the reactance of the line is 
not excessive or the line loss unusually high. For example, the constants 
should not be applied at 125 cycles if the largest conductors are used and 
the loss 20 per cent or more of the power delivered. At lower frequencies, 







♦TABLE VIM 

Data for Calculating Transmission Line Factors 


POWER TRANSMISSION 


37 


(a 

O 

00 

a 

0 

a 

ai 

> 





no 

CI 

<M 



O 

CI 

CO 

I- 



00 

rH 






i> 

02 

00 


o 

+-> 

1 C 

GO 

rH 

no 

cO 


O 






03 






pH 





fa 

o 

fca 

o 

& 

o 


rH 

no 

TtH 

cc 

o 

02 

rH 

no 

CO 

a 

P 

a 

Pa 

aa 

fl 

rH 




V 





> 

o 


no 

CO 

rH 


o 

Pa 

1 C 

02 

o 

rH 

no 

CO 




o 

o 

00 



o 

o 

no 

lO 



i-H 


• 

• 




rH 




u 

O 

—- 

w 

a3 

Pa 

t- 

V 

is 

o 

Pa 

+-> 

a 

<D 

V 

Pa 



o 

o 

o 

o 

00 

02 

02 

00 

CO 

CO 

CO 


CO 

rH 

rH 


o 

o 

o 

to 

o 

o 

o 

oo 

o 

no 

no 


CO 

rH 

rH 


o 

o 

o 

o 

CO 

CO 

CO 

02 

CO 

CO 

CO 


<M 

rH 

rH 


o 

o 

o 

ic 

o 

o 

o 

02 


CI 

CI 


ci 

rH 

rH 


o 

o 

o 

o 

CO 

00 

00 

o 

?H 

rH 

©_ 

CD 


CI 

rH 

rH 


03 

d & 
>° 


"tf 

00 

CO 

o 

o 

o 

CO 

Cl 

02 


S 

B 

H 

03 

!h 

02 


O 

I 

ta 


02 

la 


0> 

02 

Sa 


5 -G 


02 

m 

c3 

A 


02 

02 


02 

02 

o3 


Da ^3 

I 

02 


Ci r& 

a 

I 


cq 

5a 

o 

03 

« 

P 

►2 

■< 

> 


O 

>» 

o 

to 

<N 


02 

>> 

o 

o 

o 


cq 

(a 

O 

03 

a 

P 

a 

aj 


8Uiqo 

•O oSS 
000 ‘I J °d 
jo oouRjsxsaji 


Da 

'M o £ 
g £ -2D 
ic H H 


o 

o 

rj< 


>> 

u 

lO 



02 <tf 

t - iO 


ta CO 

rH rH 

co ta 

d o 

o 

00 

rtf 02 

to d 

02 i> 

no tP 

CO d 

rH O 

o o 

CO CI 

d d 

rH rH 

rH rH 

rH rH 

rH rH 

rH rH 


!>• 

O CO 

oo o 

co o 

O rH 

Hi 02 

rtf O 

iO 

00 

Cl 1 ^ 

rH 

00 l> 

no tfa 

co d 

rH O 

o o 

CO d 

ci d 

rH rH 

rH rH 

rH rH 

rH rH 

rH rH i 


CO 00 

00 CO 

«0 O 

CO no 

I- o 

Hi O 

CO CO 

o 

00 rtf 

rH O 

I- CO 

rtf CO 

d d 

rH rH 

o o 

02 

CI d 

d rH 

rH rH 

rH rH 

rH rH 

rH rH 

rH rH 


no 00 

CO r-a 

co no 

no b- 

i-a cO 

d 02 

CO rtf 

n> 

co o 

00 l> 

no rtf 

CO d 

d i-a 

rH O 

o o 

o 

d d 

rH rH 

rH rH 

rH rH 

rH rH 

rH rH 

rH rH 


02 lO 

CO 02 

co co 

b- o 

rtf o 

o o 

o o 

o 

O 02 

CO H 

CO d 

rH rH 

o o 

o o 

o o 

CO 

d i-H 

rH rH 

rH rH 

rH rH 

rH rH 

rH rH 

rH rH 

1C 

00 

02 

O CO 

rtf no 

00 rH 

CO d 

o o 

o o 

02 b- 

CO H 

CO d 

rH rH 

o o 

o o 

o o 


rH rH 

rH rH 

rH rH 

rH rH 

rH rH 

rH rH 

rH rH 


rtf CO 

d o 

o CO 

t- d 

00 rtf 

d o 

o o 

o 

00 CO 

no rtf 

CO Cl 

rH rH 

o o 

o o 

o o 

02 

rH rH 

rH rH 

rH rH 

rH rH 

rH rH 

rH rH 

rH rH 


d 02 

Tf r-a 

rtf 00 

rtf i-a 

oo no 

CO d 

O O 

lO 

CO HI 

CO CO 

d H 

r— i rH 

O O 

o o 

o o 

02 

rH rH 

rH rH 

rH rH 

rH rH 

rH rH 

rH rH 

rH rH 


rH 

I ^ CO 

I - o 

no o 

o o 

oo 

o o 

o 

CO 

CO lO 

CO d 

rH rH 

O O 

o o 

o o 

o o 

rH rH 

rH rH 

rH rH 

rH rH 

rH rH 

rH rH 

rH rH 

to 

GO 

i —1 00 

no co 

00 Cl 

I - co 

o o 

o o 

o o 

CO H 

CO d 

rH rH 

o o 

o o 

o o 

o o 


rH rH 

rH rH 

rH rH 

rH rH 

rH rH 

rH rH 

rH rH 


CO i-H 

d rtf 

I- d 

00 co 

i-a O 

o o 

o o 

o 

no H 

CO d 

rH rH 

o o 

o o 

o o 

o o 

o 

rH rH 

rH H 

rH rH 

rH rH 

rH rH 

rH rH 

rH rH 


CI o 

no 02 

rtf i-a 

la no 

CO d 

i-a O 

o o 

»o 

no H 

d r-a 

rH H 

o o 

o o 

O O 

o o 

02 








rH rH 

rH rH 

rH rH 

rH rH 

rH rH 

rH rH 

rH rH 


H H 

CO 02 

co o 

oo 

o o 

o o 

o o 

o 

GO 

CO d 

rH O 

o o 

o o 

o o 

o o 

o o 


rH rH 

rH rH 

rH rH 

rH rH 

rH rH 

rH rH 

rH rH 

»o 

GO 

CO H 

co O 

no d 

o o 

o o 

o o 

o o 

CO d 

rH rH 

O O 

o o 

o o 

o o 

o o 


r-a i-a 

rH rH 

rH rH 

rH rH 

rH rH 

rH rH 

rH rH 


02 d 

CO r-a 

ta -tf 

d Q 

o o 

o o 

o o 

o 

o 

d d 

rH rH 

o o 

O O 

o o 

o o 

o o 


rH rH 

rH rH 

rH rH 

rH rH 

rH rH 

rH rH 

rH rH 


co oo 

rtf o 

b- no 

CO d 

o o 

o o 

o o 

1C2 

02 

d r-a 

rH rH 

o o 

o o 

o o 

o o 

o o 

rH rH 

rH rH 

rH rH 

rH rH 

rH rH 

rH rH 

rH rH 


02 GO -tf f>- 
02 d C2 02 

rti co 02 

o o o o 


CO 02 
CI to 


CI ^ 

o *0 

CI CI 


02 CO 
i-a O 
CO atf 


O lO 
1—I CO 
to CO 


CO 

rH i—a 

00 O 


•sqi-u 
000‘I d 8-HAY 
aj«Q[ jo jqSta^Y 

641 

509 

403 

320 

253 

202 

159 

126 

100 

79.5 

62.8 

50.4 

39.4 

31.5 


o o 

o o 

o o 

o o 

o o 

o o 

88 

spiM jninoaif) 

o o 

o o 

o o 

o o 

o o 

o o 

o o 

o o 

no CO 

^ CO 

I-a ci 

co 

O tfi 

8-HAY }° B8JV 

Cl 00 

CO CO 

CO CO 

Cl r-a 

CO CO 

O CO 

CO o 

i—i cO 

CI I-a 

co o 

rH rH 

00 CO 

no rtf 

CO d 

d i-i 

rH rH 


oanRo s # a 

8J !M J° °N 


oo oo 
oo o 
oo 

Q_ 


i-ad CO ^tf nOcO t^OO 020 


♦Iasued by Genjial Electric Company. 



















































































38 


POWER TRANSMISSION 


however, the constants are reasonably correct even under such extreme con¬ 
ditions. They represent about the true values at 10 per cent line loss, are 
close enough at all losses less than 10 per cent, and often, at least for frequen¬ 
cies up to 40 cycles, close enough for even much larger losses. Where the 
conductors of a circuit are nearer each other than 18 inches, the volt loss: 
will be less than given by the formulas, and if close together, as with multiple- 
conductor cable, the loss will be only that due to resistance. 

The value of T depends on the system and power factor. It is equal 
to 1 for continuous current and for single-phase current of 100 per cent power 
factor. 

The value of A and the weights of the wires in Table VIII are based on 
.00000302 pound as the weight of a foot of copper wire of one circular mil 
area. 

Note. —In using the above formulas and constants, it should be par¬ 
ticularly observed that p stands for the per cent loss in the line of the delivered 
power , not for the per cent loss in the line of the power at the generator; a d 
that E is the potential at the delivery end of the line and not at the generator. 

When the power factor cannot be more accurately determined, it may 
be assumed to be as follows for any alternating system operating under average 
conditions: Incandescent lighting and synchronous motors, 95 per cent; 
lighting and induction motors together, 85 per cent; induction motors alone, 
80 per cent. 

In continuous-current three-wire systems, the neutral wire for feeders 
should be made of one-third the section obtained by the formulas for either 
of the outside wires. In both continuous and alternating-current systems, 
the neutral conductor for secondary mains and house wiring should be taken 
as large as the other conductors. 

The three wires of a three-phase circuit and the four wires of a two-phase 
circuit should all be made the same size, and each conductor should be of 
the cross-section given by the first formula. 

Numerical examples of the application of Table VIII, as well 
as of other formulas, are given later. A better idea of the way in 
which the different quantities involved affect the regulation of an 
alternating-current line may be obtained from graphical repre¬ 
sentation or from formulas which are not so empirical. Before 
taking up other methods of calculation, however, let us consider 
the meaning of power factor. 

By power factor we mean the cosine of the angle by which the 
current lags behind or leads the electromotive force producing 
that current. It is the factor by which the apparent w T atts—volts 
times amperes—must be multiplied to give true power. The formula 
for power in a single-phase circuit is 

Power = IE cos 0 

where 0 is the lag or lead angle; and for three-phase circuits 


POWER TRANSMISSION 


39 


Power = IE cos 0 V 7 3 

where I is the current flowing in a single conductor. 

For two-phase circuits, balanced load, this becomes 

Power =2 IE cos d 
and for six-phase circuits 

Power=2 V 3 IE cos 0 

% 

For single- and three-phase circuits E is the voltage between 
lines; for two-phase circuits it is the voltage across either phase; 
and for six-phase circuits it is the voltage across one phase of what 
corresponds to a three-phase connection. If voltage is taken from 
line to line in the six-phase system 

Power =6 El cos 0 


Considering the formula for single phase, we find that the 
current flowing in the line may be taken as made up of two com¬ 
ponents, one in phase with 
the voltage and one 90 de¬ 
grees out of phase, lagging, 
or leading, depending on 
conditions. In Fig. 24, let 
OE equal the impressed 
pressure and OC the current 

flowing. 6 is the angle of lag. The current OC may be resolved 
into two components, one in phase with OE— OB, and one 90 degrees 
behind 0E=BC. 

OB=OC cos 0 



Fig. 24. Vector Diagram for Single-Phase System 


is known as the active component of the current. 

BC= OC sin 0 

is known as the wattless component of the current. 

The capacity and inductance are distributed throughout the 
line, that is, the line may be considered as made up of tiny con¬ 
densers and reactance coils, connected at short intervals as shown 
in Fig. 25. Considering the inductance and capacity as distributed 
in this manner, the regulation of a system may be calculated, but 
the process is very difficult, and simpler methods, which give very 
close results, have been adopted for practical work. Probably the 






40 


POWER TRANSMISSION 


methods presented by Perrine and Baum are as simple as any ex¬ 
cept those based on purely empirical formulas.^ 

Tables giving the capacity and inductance of lines, together 
with the formulas for the calculation of these quantities, have 



Fig. 25. Diagram of Distribution of Capacity and Inductance Throughout the Line 


already been given. It has also been stated that the effect of the 
capacity of a line is to cause a charging current to flow in the line, 
this current being 90 degrees in advance of the impressed voltage. 
The value of this charging current is 


Charging current per wire= 


EXCX2nXf 

2X10° 


single-phase 


where C is capacity in microfarads of one wire to neutral point; 
/ is frequency of the circuit; and E is voltage between wires. 

2 

Charging current, three-phase, = —- or 1.155X charging cur¬ 
rent, single-phase. 1 ^ 

Since the voltage across the lines is not the same all along 
the line, the value of the charging current will not be the same, 
but the error introduced by assuming it to be constant is not great. 
For our calculation, then, we assume that the charging current in 
an open-circuited line is constant throughout its length, and also 



Fig. 26. Diagram of Single-Phase Line 


that the capacity of the line may be taken as concentrated at the 
center of the line. 

Consider a single-phase line such as is shown diagrammatically 
in Fig. 26. Let E 0 be the voltage at the generator end of the line; 
E, the voltage at the receiver; L, self-induction of the line; 7 c , charg¬ 
ing current per wire; 7, current flowing in the line due to the 
load on the line; 0 , angle by which the load current differs from 




















POWER TRANSMISSION 


41 


the impressed voltage; R, resistance of the line; e, drop in voltage 
in the line; co, 2 7 if. 

+j is a symbol indicating that the current is 90 degrees in ad¬ 
vance of the pressure. 

— 7 indicates that the current is 90 degrees behind the pressure. 

The expression, ^R 2 + ( 2 i r/L) 2 = ^ R 2 + co 2 L 2 may be repre¬ 
sented by R-\-jLco, the factor -\-j indicating that the square root 
of the sum of the squares of these two quantities must be taken 
to obtain the numerical result. The quantity j 2 may be considered 
as —1. 

Taking the capacity of the line and considering it as a con¬ 
denser located at the middle of the line, we may assume the charg- 

W 

b 


Fig. 27. Vector Diagram of Quantities Involved in Single-Phase 

ing current as flowing over only one-half of the line, or one-half the 
charging current may be considered as flowing over all of the line. 

Let the impedance of the line equal 1 R 2 -\-co 2 L 2 = R-\-jL(o; 
the power factor of the load equal cos d; the active component of 
the current equal 7 cos 6 ; the wattless component of the current 
equal —jl sin 6 {—j indicating that the current lags 90 degrees be¬ 
hind the pressure). j 

The charging current may be represented by +j .—-. Then the 
drop due to the active component of the load is 

I cos 0 (R+jLty) 











42 


POWER TRANSMISSION 


The drop due to the wattless component of the load is 


— jl sin 6 {R-\-jL(o) 

The sign of this term will be positive if the load current leads the 
voltage. The drop due to the charging current is 

+i-^ (R+jLco) 


The total drop is equal to the sum of these three values, or e, 
so that 

E q = E-\-e= E-\-I cos 6 (R-\-jLco)—jI sin 6 (R-\-jL(o) 

+i-~ (R+jLco) 


Expanding this and substituting — 1 for j 2 we have 

E 0 =E+I cos 0 R+jl cos 0 Leo—jl sin 0 R+7 sin 0 Lw 


I I 

+j i~ R ~ ~f Loj 


Referring to Fig. 27, we have these various values plotted 
graphically. 


oa — E 


ab =+j- 


IR 


bc= — 


I Leo 
2 


cd= + 7 cos 0 R de= -f jl cos 0 Leo 

ef= — jlR sin 0 fg= -\-ILuj sin 0. 

og=E 0 

ab is plotted 90 degrees in advance of oa on account of the symbol 

+i- 

be is plotted in the opposite direction from oa on account of the 
negative sign. 

ef is plotted downward on account of the symbol —j. 

If we let oa', Fig. 27, represent the current vector, then 0 equals 
angle of lag, and eg, which equals IR, is plotted parallel to oa', and 
ce, which equals ILco, is plotted perpendicular to oa'. 

It is seen from this that the charging current tends to pro¬ 
duce a rise in the electromotive force instead of a drop in pressure. 

The above takes into account only the constants of the line. 
In order to determine the regulation of a complete system, the 
resistance, capacity, and inductance of the translating devices must 



POWER TRANSMISSION 


43 


be considered as well. A diagram of a complete system with both 
step-up and step-down transformers connected in service is shown 
in Fig. 28. The charging current may be considered as flowing 



Fig. 28. Diagram of Complete Single-Phase System, with Transformers in Service 


through half of the system only, viz, the generator, the step-up trans¬ 
formers, and one-half of the line. 

Let R l equal the equivalent resistance of the step-down trans¬ 
formers; R 2 equal the equivalent resistance of the step-up transform¬ 
ers; L v equal inductance of the step-down transformers; L, equal 
inductance of the step-up transformers; R g equal equivalent resist¬ 
ance of the generators; L g equal equivalent inductance of the genera¬ 
tors; R equal resistance of the line; L equal inductance of the line; 
L t equal L i + L 2 + L g + L; and R T equal R t + R 2 + R g + R. 

All quantities should be converted into their equivalent values 
for the full line pressure. Thus, the generator and receiver voltages 
should be multiplied by the ratio of transformation of the step-up 
and step-down transformers, respectively, to change them to the 
full line pressure. The resistance and inductance of the transformers 
must include the resistance and inductance of both windings, and 
the value must correspond to the line voltage. Thus, the resistance 
of the step-up transformers will be 

r x n 2 + r 2 

where r y equals the resistance of the primary coil; r 2 equals the 
resistance of the secondary coil; and n equals the ratio of transfor¬ 
mation. The equivalent resistance of the step-down transformers 
will be 

7*1 + ft 2 r 2 

The generator resistance and inductance must be multiplied by 
n 2 to bring them to equivalent values for the full line pressure. 

The formula then becomes 

E 0 = E + I cos 0 (R t + j L t oj) — j I sin 0 {R T + j L T co) 

+ i Ic [XlT + + (~2~ + + A;)] 








44 


POWER TRANSMISSION 


Referring to Fig. 27, we have these various values plotted 
graphically: 

ca = E 

ab = j if j+R 2 + /?„) 

be = —l c w (-g- + L 2 + 

The numerical value of E and E o may be determined from a 
diagram such as is shown in Fig. 27, when constructed to scale; 
or it may be calculated analytically, remembering that the quan¬ 
tities affected by j are to be combined, geometrically, with the 
quantities not affected by the symbol, that is, the numerical value 
is the square root of the sum of the squares of the quantity not affected 
by j and the quantity affected by j. 

The above formulas apply to single-phase circuits directly. 
If they are to be used for the calculation of three-phase circuits, the 
following points must be observed: 

2 

1. Charging current I c , three-phase=^ 77 ^= X charging current single-phase. 

2. The voltage should preferably be considered as the voltage between 
one line and the neutral point. The voltage to the neutral point will be the 
line voltage divided by 

3. The resistance of one line only is considered, not the resistance of 
a loop. 

4. The inductance of one line only is used. The inductance of one line 
equals the inductance of a loop divided by \/T. 

5. Three-phase systems may be calculated by considering them as single¬ 
phase systarcs with two wires of the same size and spacing but with only 
one-half the amount of power transmitted. 

Examples. 1. What is the capacity, in microfarads, between 
wires of a single-phase transmission line 10 miles in length com¬ 
posed of No. 6 copper wires spaced 15 inches apart? What is the 
capacity to the neutral point? 


cd = I cos 6 R t 

de = j I cos 6 L t eo 
ef = — j I R t sin 0 

fg = I L r co sin 6 
°9 = E o 


C in microfarads= 


19.42 X 10~ 3 



per mile of circuit 



POWER TRANSMISSION 


45 


A =15 inches 

?4=185 

a 

C in microfarads= 
with respect to the neutral point 

C in microfarads = 


d= .162 inches 
log 185=2.2672 
19.42 X 10 


2.2672 

.0776 


2 log 


2 A 
d 

.0776 


X 10 = .085 


' 2 X 2.2672 


X 10= .171 


This shows that the capacity to the neutral point is twice the capacity 
to the other wire. 

2. What is the self-inductance of one loop of the above circuit 
assuming it to be a three-phase instead of a single-phase system? 


L = .000558 


[2.303 log 


2A 

d 


+ 25^ P er m ^ e 
' circuit 


= .000558 (2.303 X 2.2672 + .25) X 10 
= .000558 X 5.47 X 10 = .0305 henrys 


3. A circuit has a capacity of .2 microfarads. What must 
be the value of its inductance to compensate for this capacity at 
60 cycles? 

r _ i , _L_ 

(2 n jY L’ 01 y (2nfyc 

in which C= .0000002 farads; (2 ?r ff= (2X3.1416X60) 2 = 142,122, 
:.L = 1-5- (142,122 X .0000002) =35.2 henrys. 

4. It is desired to transmit 1,000 kw\ a distance of 25 miles 
at a voltage of 20,000, a frequency of 60 cycles, and a power factor 
of 85 per cent. Transmission is to be a three-phase three-wire system. 
Allowing 10 per cent loss of delivered power in the line, it is required 
to find (a) area of conductor, (b) current in each conductor, (c) volts 
lost in line; and (d) pounds of copper. 


Area of conductor 


DXWXC' 

pXE 2 


in which D= 25X5,280= 132,000; W= 1,000X1,000= 1,000,000; C' 








46 


POWER TRANSMISSION 


= 1,500 for three-phase three-wire system and 85 per cent power 
factor; p=10; E= 20,000; and E 2 = 400,000,000. 

132,000X1,000,000X1,500 


Area of conductor = 


10X400,000,000 
132X1,500 


= 49,500 circular mils 


No. 3 wire has a cross-section of 52,630 circular mils. 

WX T 

Current in each conductor= 


E 

in which T = .68 for three-phase system, 85 per cent power factor. 

„ . 1,000,000 X .68 0/i 

Current in each conductor = --= 34 


Volts lost in line = 


20,000 
pX EXB 

Too 


in which B= 1.18 for No. 3 wires, 60 cycles and 85 percent power 
factor. 


Volts lost in line = 


10 X 20,000 X 1.18 
100 


= 2,360 


D 2 X W X C' X A 
Pounds copper= pXFxl 000)0(MJ 

or it may be calculated directly from the weight of wire given in 
the tables after the size of wire has been determined by other formulas. 
Thus 75 miles of No. 3 wire is required. This weighs 159 pounds per 
1,000 feet. 

159 X 5.280 X 75 = 62,964 pounds 


5. A single-phase line 20 miles in length is constructed of 
No, 000 wire strung 24 inches apart. It is desired to transmit 
500 kw. over this line at a frequency of 25 cycles and a power factor 
of 80 per cent, the voltage at the receiver end being 25,000. Con¬ 
sidering the line drop only, what must be the voltage at the generator 
end of the line? 


E 0 =E+7 cos 0 R-\-j I cos 0 Lco—j I sin 0 R 

+ 7 sin 0La> + j — R — — L <o 
2 2 









POWER TRANSMISSION 


47 


in which E = 25,000; = 


Cos 0=.8O; sin 0 = .60 (from trigonometric tables); R= resistance 
of 40 miles of No. 000 wire= 14.56 ohms at 50° C; L= .00277 X 

-7=X20=.064 (calculated from Table VII); co = 2xf = 2 kX25= 157; 
V o 


EX CX 2nXf 
2 X 10 6 


25,000 X .3752 X 157 

2 X 1,000,000 


= .736 amperes; and 


C=.3752 (Table VI, or calculated) 


Substituting these values in the above formula we have 


E 0 = 25,000 + -291.2 + J200.8 - J218.4 + 150.6 + j5. 36 - 3.7 
E = 25,000 + 291.2 + 150.6 - 3.7 + +200.8 - 218.4 + 5.36) 

E = 25,000+291.2 + 150.6 - 3.7 + j(218.4 - 200.8 - 5.36) 

Since the symbol j indicates that the quantities must be com¬ 
bined geometrically, then 

E 0 = 1/(25,000+ 291.2+ 150.6 - 3.7) 2 + (218.4 - 200.8 - 5.36) 2 
E= V (25,438.1) 2 + (12.24) 2 = 25,438.1 volts 
6. A three-phase line 20 miles in length is constructed 
of No. 000 wire strung 24 inches apart. We wish to transmit 
1,000 kw. over this line at a frequency of 25 cycles and a power 
factor of 85 per cent, the voltage at the receiving end being 2,000. 
Three Y-connected 500-kw. transformers having a ratio of 10 : 1, 
step the voltage up and down at either end of the line. The resist¬ 
ance of the high-tension winding of each transformer is 4 ohms. 
The resistance of the low-tension windings is .04 ohms. The in¬ 
ductance of each transformer is .4 henrys. Neglecting the generator 
constants, what must be the voltage applied .to the low-tension 
windings of the step-up transformers? 

E 0 = E +1 cos 0 (R t + j L t oj) - j I sin 0 ( R T + j L t oj) 

+ i Ic [ (-g" + ^ 2 ) + fo (~2"+ L 2 ) J 


Since this is for a three-phase circuit we will work with the 
voltage to the neutral point and will change all values to corre¬ 
spond to the line voltage. Hence, 


•Power = IE cos 0 . 








48 


POWER TRANSMISSION 


Eq__ 

V 3 


X 10 


E 

l/l 


X 10 + 


7 = 34 amperes 


Since V 3 IE Cos 0 = 1,000,000 
22 = 10 X 2,000 = 20,000 
Cos 0 = .85 
7= 34 


R t = Resistance of one line + equivalent resistance of one 
transformer at each end of the line. 

R t = 7.28 ohms + 4 + 100 X .04 + 4 + 100 X .04 
= 23.28 ohms 

L T = .0554 V 3 + .4 + .4 = .832 henrys 
o)~ 157 
sin 0 =.52 

2 

7 c = .589 X ■ /-= = -077 amperes = charging current single- 

1 o 

2 

phase X-j/y . 

f = 3 ' 64 


#2 

2 


= 8 
= .016 


l 2 = a 


Substituting these values in our formula, we have 
E 0 X 10 _ 20,000 


_ f 672.8 + j 3774 - j 411.6 + 2309+ j 7.88 - 44.2 

1. /o 1. to 

= 11,550 X 672.8 + 2,309 - 44.2 + j (3,774 - 411.6 + 7.88) 


= V 14,487.6 2 + 3,370.3 2 = 14,874 
E q = 2,573 volts 

7. A three-phase transmission line 40 miles in length delivers 
10,000 kw. at 40,000 volts, power factor 85 per cent, frequency 
60 cycles. The line consists of three aluminum conductors of a cross- 
section equivalent to No. 0000 wire, spaced 42 inches apart. Re¬ 
quired the potential at the generator end of the line, neglecting 
charging current. 

Solving this as a single-phase circuit, we can assume 5,000 kw. 
transmitted over two conductors spaced 42 inches. 











POWER TRANSMISSION 


49 


The resistance of one mile of conductor is .432 ohm, or a total 
resistance for the line of 80X .432= 34.56 ohms. 

The inductance of a loop is calculated as follows: 

L= .000644 [2.303 log^+ .25] X 40 

= .000644 [2.303 log ~ + .25] X 40 

(No. 0000 stranded cable has a diameter of .522 inch.) 

= .000644 X 213.2 
= .1373 henrys 

oj = 27if=2X 3.1416 X 60 = 377 
I = 147 amperes 

E 0 = E + I cos 0 (R + j Leo) — j I sin 0 (R + j Leo ) 

I cos 0= 147 X .85 = 125 
I sin 6= 147 X .53 = 77.9 
R+jLco = 34.56+ (j 377 X .1374) = 34.56 +j 51.8 
= V (34.56 ) 2 + 51.8) 2 = 62.1 
E 0 = 40,000+ (125 X 62.1)- (j 77.9 X 62.1) 

= 47762.5 - j 4837.6 
= V (47762.5) :2 + (4837.6) 2 
= 48,006 volts 

TRANSFORMERS 

A transformer consists of two coils made up of insulated wire, 
the coils being insulated from each other and from a core, made 
up of laminated iron, on which they are placed. One of these coils, 
known as the ‘primary coil, is connected across the circuit, in con¬ 
stant-potential transformers, and the other coil, known as the 
secondary coil y is connected to the lamps or motors, or whatever 
makes up the receivers. As a matter of fact, these coils are each 
usually made up of several sections. The voltage induced in the 
secondary windings is equal to the voltage impressed on the pri¬ 
mary winding multiplied by the ratio of the number of turns in 
the secondary to the number in the primary coil, less a certain drop 
due to impedance of the coils and to magnetic leakage. This drop 
is negligible on no load. If transformers are used to raise the voltage, 
they are termed step-up transformers. If used to lower the voltage, 
they are called step-down transformers. 




50 


POWER TRANSMISSION 


Power Losses. Loss.es of power occurring in transformers are 
of two kinds, namely, iron, or core, losses which are made up of hystere¬ 
sis and eddy-current losses in the iron making up the core, and copper 
losses which are due to the PR losses in the windings with the addi¬ 
tion, in some cases, of eddy currents set up in the conductors them¬ 
selves. 

Efficiency. The efficiency of a transformer depends on the 
value of the power losses and may be expressed as the ratio of the 
watts output to the watts input. 

W 8 _ W- (W'+W k +W) 

K w. 

Where W s = watts secondary; W p = watts primary; W c — copper losses; 
W h — hysteresis losses; and W e = eddy-current losses. 


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Fig. 29. Y Connections for 
Transformers 


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Fig. 30. A Connections for 
Transformers 


The iron losses remain constant for any given voltage regard¬ 
less of the load, while the copper losses are proportional to the 
square of the current. The efficiencies of transformers are high, 
varying from 94 to 95 per cent at f load to 98 per cent at full load 
for sizes above 25 kw. 

All-Day Efficiency. By all-day efficiency is meant the efficiency 
of a transformer, taking into consideration its operation for twenty- 
four hours, and it is calculated for the ratio of watt-hours output 
to watt-hours input for this length of time when in actual service. 










POWER TRANSMISSION 


51 



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Fig. 31. Vector Diagrams of Step-down Transformers by Y and A Systems— 

Primary Voltage 1,000 


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Fig. 32. Diagram of Scott Connections and Vector Diagrams for Same 












































































52 


POWER TRANSMISSION 


For calculation, the transformer is often assumed to be fully loaded 
for five hours and run with no load for the remaining nineteen. 
The all-day efficiency is then determined as follows: 

Output, kw. hours = watts output at full load X 5 

Input, kw. hours = (watts output at full load Xo) + (I 2 R loss at 
full load X 5)+ (core loss at normal voltage X 24) 

, . output, watt-hours 

All-day efficiency =7 -;- 

input, watt-hours 

The assumption that a lighting transformer is fully loaded 
five hours out of the day is not always a correct one. On many 

circuits from two to three 
hours of full load would 
be more nearly the proper 
value to use in calculating 
the all-day efficiency. 

If the efficiency of a 
transformer is low, it means 
a direct loss of considerable 
energy as well as greater 
heating of the transformer 
and consequent deteriora¬ 
tion. If a transformer is 
to be used for lighting pur¬ 
poses, or is lightly loaded 
for a large portion of the 
time, a type which has a re¬ 
latively low core loss should 
be selected so as to increase 
the all-day efficiency. If 
fully loaded all day, the 
losses should be divided about equally between the copper and the 
iron losses. 

Regulation. By regulation of a transformer is meant the 
percentage drop in the secondary voltage from no load to full load 
when normal pressure is impressed on the primary. This drop is 
due to the IR drop in the windings and to magnetic leakage. In 
well-designed transformers the loss due to magnetic leakage is about 






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POWER TRANSMISSION 


53 






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10 per cent, or less, of that due to the resistance drop. For non- 
inductive load (power f actor = unity) the regulation is from 1 to 3 
per cent in good transformers. With induction load this is increased 
to 4 or 5 per cent, or even more. 

Regulation should be considered carefully in selecting a trans¬ 
former for given service. Thus, if a transformer is to be used for 
lighting, its regulation should be of the best, since drop in voltage 
due to the transformer is in addition to that due to the conductors. 
In the same way the regulation of any system as a whole depends 
to a certain extent on the regulation of the transformer installed. 

Connections. Transformers for three-phase work may be con¬ 
nected in two ways. Where three transformers are used, they may 
be connected in Y or star, 
that is, with one terminal 
of each primary brought to 
a common point and the 
other terminal connected 
to a line wire, Fig. 29, or 
they may be connected in 
A or mesh when the three 
primaries are connected in 
series and the line wires 
are connected to the three 
corners of the triangle so 
formed, Fig. 30. The sec¬ 
ondaries may be connected 
in Y the same as the pri¬ 
maries, or the secondaries 
may be connected in Y when 
the primaries are in A, or 
vice versa. The voltage re¬ 
lation may best be determined from vector diagrams, as shown in 
Fig. 31, which give the voltage relation of step-down transformers with 
a ratio of 10:1, when the voltage across the primary lines is 1,000. 

Changes from two to three phases, or from three to two phases, 
with or without a change of voltage, may be made with transformers 
having the required ratio of transformation by use of the Scott 
connections. Fig. 32 shows such a connection together with a corre- 



Fig. 34. 


Six-Phase Y Circuit for Transformer with 
Two Secondaries 














54 


POWER TRANSMISSION 


sponding vector diagram showing the relations when the change 
is from two phases to three phases with a 10:1 transformation of 
voltage. The main transformer is fitted with a tap at the middle 
point of the secondary winding to which one terminal of the teaser 
transformer is connected. The teaser has a transformation ratio 
differing from that of the main transformer, as shown in the figure. 

Six phases are obtained from three phases for use with rotary 
converters by means of transformers having two secondary wind¬ 
ings or by bringing both ends of each winding to opposite points on 
the rotary converter winding, utilizing the converter winding for 
giving the six phases. This transformer connection, Fig. 33, is known 
as a diametrical connection. When transformers with two secondaries 
are used, the secondaries may be connected in six-phase Y or six- 

phase A, as shown in Figs. 
34 and 35. When the Y- 
connection is used, the com¬ 
mon connection of each set 
of secondaries is made at the 
opposite ends of the coils. 
This leaves the free ends di¬ 
rectly opposite, or 180 de¬ 
grees different in phase. The 
way in which these ends are 
brought out to give six phases 
is best illustrated by means of 
the two triangles arranged as 
shown in Fig. 36, which have 
their points numbered corre¬ 
sponding'to the connections 
in Fig. 34. In Fig. 35 one A is 
reversed with respect to the 
other, and six phases are 
brought about in this manner. 

Single transformers, constructed for three-phase and six-phase 
work, are now manufactured in this country, and are being used to 
an increasing extent. They are a little cheaper to build for the same 
total output, and save floor space, but are not so flexible as three 
single-phase transformers. ' 






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Fig. 35. ~ Six-Phase A Circuit for Transformer with 
Two Secondaries 




















POWER TRANSMISSION 


55 


Where other conditions allow, a A-connection to A-connection 
is preferable, for with this connection, if one transformer is injured, 
it may be taken out of circuit and the remaining two will maintain 
the service, and may be loaded up to .57 of the former capacity of 
the system. In the Y-connection, however, the voltage impressed on 


the transformer winding is only = .58 

times the voltage of the line, thus making it 
possible to construct a transformer with a 
fewer number of turns. The windings must 
be insulated from the case, however, for a 
potential equal to the line potential, unless 
the neutral point be grounded when the po¬ 
tential strain to which the transformer is oe 11A „ w , 

Fig. 36. A Diagram cf 

liable to be subjected, under ordinary condi- Si se^ondli^ r arcui™ er 

tions, is reduced to —°f its value when the neutral is not 



grounded. For small transformers wound for high potential the cost 
is in favor of the Y-connection. 

Choice of Frequency. The frequencies in extended use in this 
country at present are 25, 40, and 60 cycles, 25 or 60 cycles being 
met with more frequently than 40 cycles. Formerly a frequency 
of 125 or 133 cycles per second was quite often employed for light¬ 
ing purposes, but these are no longer considered standard. 

The advantages of the higher frequency are: ' 

(1) Less first cost and smaller size of generators and transformers for 
a given output. 

(2) Better adapted to the operation of arc or incandescent lamps. Lamps, 
when run below 40 cycles, especially low candle-power incandescent lamps at 
110 volts or higher, are liable to be trying to the eyes on account of the flicker. 


The disadvantages of the higher frequency are: 

(1) Inductance and capacity effects are greater, hence a poorer regu¬ 
lation of the voltage. The charging current is directly proportional to the 
frequency and this amounts to considerable in a long line. 

(2) There is greater difficulty in parallel operation of the high- 
frequency machines due to the fact that the armature reactions of the older 
types of high-frequency machines are high. 

(3) Machines for high frequencies are not so readily constructed for 
operation at slow speeds. This, however, will cease to be an objection with 
the increasing use of the steam turbine. 






56 


POWER TRANSMISSION 


(4) Not well adapted to the operation of rotary converters and single¬ 
phase series motors on account of added complications in construction and 
increased commutator troubles. 

A frequency of 60 cycles is usually adopted if the power is to 
be used for lighting only, and 25 cycles are better for railway work 
alone. By the use of frequency changers the frequency of any sys¬ 
tem may readily be changed to suit the requirements of the service. 

OVERHEAD LINES 

Having considered the calculation of the electrical constants 
of a transmission line and distributing system, we turn next to the 
mechanical features of the installation of the conductors and find 
two general methods of running the wires or cables, viz, 

(1) The conductors are run overhead and supported by insulators 
attached to pins in cross-arms which, in turn, are fastened to the supporting 
poles. 

(2) The cables are placed underground and are supported and pro¬ 
tected by some form of conduit. 

Overhead construction is used when the lines are run through 
open country or in small towns. It forms a cheap method of pro¬ 
viding satisfactory service and is reliable when carefully installed. 
It has the advantage that the wires may be placed some distance 
apart and, being air-insulated, the capacity of the line is much less 
than that of underground conductors. 

The old practice in overhead line construction has always been 
to consider the design and the erection of the line as work that any one 
could do, it being taken as the simplest part of the electrical system. 
As a result, the line was a source of much trouble which was laid to 
almost any other cause than poor construction. The overhead line, 
when used, must be considered as a part of the power plant and it 
should receive as careful attention as any part of the central station 
or substation. It often has to meet much more severe conditions 
than the power plant itself and it is responsible to a very large extent 
for the reliability of service. 

The new way of treating the question of overhead lines is to 
consider them as structures which must be designed to meet cer¬ 
tain strains just as a bridge or similar structure is designed. This 
is especially true when steel or iron poles are used as is the case 
in nearly all transmission lines abroad* 


POWER TRANSMISSION 


57 


The design of an overhead line may be divided into five parts, 
some being purely mechanical features while others are both me¬ 
chanical and electrical. 

(1) Location of line. 

(2) Poles or towers and cross-arms. 

(3) Insulators and pins. 

(4) Stresses sustained by the pole line. 

(5) Conductors. 

Location of Line. The location of the line takes into account 
the territory over which the line must be run with respect to con¬ 
tour, direction, and freedom from obstructions, as well as possible 
right of way. Width of streets, kind and height of buildings, and 
liability to interference with or from other systems must be con¬ 
sidered, when such are present. The right of way for electric lines 
may be secured, in some cases, along a railway or public road when 
its location is comparatively simple, provided it is not necessary 
to interfere with adjoining property. When adjoining property 
must be interfered with, or when the line is to run over sections 
containing no roads, it is usually possible to form contracts with 
the property owner such as shall free the line from future inter¬ 
ference by the property owner. In general, the cost of such con¬ 
tracts will be comparatively low. Again, the right of way may 
be purchased outright, as is preferable when right of way is being 
secured for high-speed electric railways. When the demands for 
right of way are in excess of a reasonable amount, the process of 
condemnation of property may be resorted to or the direction of 
the line may be changed so as to avoid such locations. A prelimi¬ 
nary survey of the line should be made at the time the route is being 
located, such a survey consisting of the approximate location of 
the poles, notes of the changes in direction and level of the ground 
as well as of its character. This survey aids in the selection of 
material to be delivered to the different parts of the line. Changes 
in level are compensated for as much as possible by selecting long 
poles for the low places and short poles for the higher elevations, 
thus reducing the unbalanced strains in the line. 

The heavier poles should be used where there is a change in 
direction, where the line is especially exposed to the wind, or where 
branch lines are taken off. It is sometimes necessary that power 


58 


POWER TRANSMISSION 


lines be run on the same poles as telephone wires, in which case the 
power conductors should, preferably, be located above the telephone 
wires. 

Poles. In this country, the support for aerial lines consists almost 
universally of wooden poles to which the cross-arms, bearing the 
insulator pins, are attached. These poles may be either 
natural grown or sawed. Abroad, the use of metal 
poles prevails. In order to determine the proper 
cross-section of a pole it may be regarded as a beam 
fixed at one end and loaded at the other, this load 
consisting of the weight of the wire, with attendant 
snow or sleet, which tends to produce compression in 
the pole, and the tension of the wires together with 
the effect of wind pressure, which tends to produce 
flexure. Only the latter stresses need be considered 
in selecting a pole for ordinary transmission lines. 
The poles are in the shape of a truncated cone or 
pyramid, Fig. 37, the equation of which is 

( '' / ' /| ) 

where y is diameter of any section; x is distance from 
_ the top of the pole; l is length of pole; and di and d 2 
are diameters of the pole at the top and bottom 
respectively. 

Taper. The proper taper for a pole should be such 
Fie Lfne Poi D e dard that ^ e q uals f of d L . If d 2 is greater than f d h 
the pole is heavier than need be, as it would tend to 
break below the ground. If d 2 is less than § d , the pole will tend 
to break above the ground and the material is not distributed to 
the best advantage. 

Size. In calculating the size of pole necessary to stand a certain 
stress, we have, from the principles of Mechanics, 



2 


where M is moment of resistance, I is moment of inertia; S is stress 
in the section at d 2 , at which point the pole is least able to withstand 














POWER TRANSMISSION 


59 


the strain which comes on it. M equals PI, where P is the tension in 
the wires and l is the length of pole in inches. 

For a round pole 



and we have 


Solving for S 


Sxd 4 2 

64 _ S7id 3 2 
~dT~ 32 
2 


S = 


32 PI 

7td\ 


For a sawed pole with square cross-sections the value of I is 



and 


Pl = 


Sd\ 

6 


or S = 


6 PI 

d\ 


The value for £ should not exceed a certain proportion of the 
ultimate strength of the material. If T represents the ultimate 


T 

strength in pounds per square inch, then P= —, where n is known as 

the factor of safety and is ordinarily not taken less than 10 for wooden 
structures. A high factor of safety is necessary on account of the 
material not being uniform, and the uncertainty of the value of T. 
Commonly accepted values of T are: 


Yellow pine. 5,000-12,000 pounds 

Chestnut. 7,000-13,000 pounds 

Cedar.11,500 pounds 

Redwood.11,000 pounds 


T 

The value of — should not be over about 800 for natural poles 
n 

and 600 for sawed poles. 

d 2 is measured at the ground line of the pole, not at the base. 
Consider a pole of circular cross-section having a length of 

T 

35 feet and a diameter at the ground line of 12 inches. Using — = 600, 












60 


POWER TRANSMISSION 


what is the maximum allowable stress that should be applied at the 
end of the pole? 



where P = 600; l — 35 X 12 = 420 inches; and d 2 = 12 


32 X 600 X 420 
3.1416 X 1728 


= 1,486 pounds 


It is customary to select a general type of pole for the whole 
line, determined from calculations based on the above formulas, 
after the tension in the wire has been found, and not to apply such 
calculations to every section of the line. The line is then reinforced, 
where necessary, by means of guy wires or struts. : \ 

Some of the general requirements for poles are: 

Spacing should not exceed 40 to 45 yards. 

Poles should be set at least 5 feet in the ground with an additional 6 
inches for every 5 feet increase in length over 35 feet. Special care in setting 
is necessary when the ground is soft. End and corner poles should be braced 
and at least every tenth pole along the line should be guyed with or f-inch 
stranded galvanized iron wire. 

Inspection. Regular inspection of poles, at least yearly, should 
be maintained and defective poles replaced. The condition of poles 
is best determined by examination at the base. 

Poles should preferably be of good, sound chestnut, cedar, or 
redwood. Other kinds of wood are sometimes used, the material 
depending largely on the section of the country in which the line 
is to be erected and the timber available. Natural poles should be 
shaved, roofed, gained, and given one coat of paint before erecting. 

Preserving. Special methods of preserving poles have been 
introduced, chief among which may be considered the process of 
creosoting. Creosoting consists of treating the poles with live steam 
at a temperature of 225° to 250° F., so as thoroughly to heat the 
timber, after which a vacuum is formed, and then the containing 
cylinder is pumped full of the preserving material, a pressure of 
about 100 pounds per square inch being used to force the desired 
amount of material into the wood. The butts of poles are often treated 
with pitch or tar, but this should be applied only after the pole is 
thoroughly dry. 




POWER TRANSMISSION 


61 


Guying. Guying of pole lines is one of the most important 
features of construction. Guys consist of three or more strands of 
wire, twisted together, fastened at or near the top of the pole, and 
carried to the ground in a direction opposite to that of the resulting 
strain on the pole line. The lower end is attached to some form 
of guy stub or guy anchor, which may be a tree, a neighboring 
pole, a short length of pole set in the ground, or a patent guy anchor. 
Guy stubs are set in the ground at an inclination such that the guy 
makes an angle of 90 degrees with the stub or with the axis of the 
stub in the direction of the guy, the stub in the latter case being 
held in place by timber or plate fastened at right angles to the bottom 
of the stub. Such a timber is known as a “dead man”. 

The angle the guy wire makes with the pole should be at least 
20 degrees. When there is not room to carry the guy far enough 





away from the base of the pole to bring this angle to 20 degrees or 
more, a strut may be used. This consists of a pole slightly shorter 
and lighter than the one to be reinforced. It is framed into the line 
pole near the top and set in the ground near the base of the pole 
on the opposite side from that on which a guy would be fastened. 

Stranded galvanized steel guy wire is used for guys. There 
are two general methods of attaching the guys to the top of the 
pole. In the one, a single guy is run, attached at or near the middle 





















62 


POWER TRANSMISSION 


cross-arm, while in the other, known as Y guying, tw T o wires are 
run to the top of the pole, one at the upper, the other at the lower 
arm, and are united into a single line a short distance from the pole. 

Head guying, that is, guying in the direction of the line, is used 
when the line is changing level and for end poles. The guys are 
attached near the top of one pole and run to the bottom of the pole 
just above. Fig. 38 shows several methods of reinforcing pole 
lines. Special methods are adapted as necessary. 

Steel Towers. Steel towers are now being used to a considerable 
extent, especially on important lines, because of their longer life and 


ar=3 

SECT/ON A A 



SECTION B3 




Fig. 39. Plan and Elevation of Steel Tower 


greater reliability. The first cost varies from two to four times 
that of wood-pole line construction. These towers take a large 
variety of forms, one of which is shown in Fig. 39. They are spaced 
8—12 to a mile on straight w r ork and range in height from 40 to 60 
feet, the higher towers being used for the longer spans. There is a 
saving in the number of insulators required over the number neces¬ 
sary for wood-pole lines. For protection and appearance the 
material of the towers is galvanized. 










































































POWER TRANSMISSION 


63 


Cross=Arms. The best cross-arms are made of southern yellow 
pine, although oak is used to a large extent. They should be of 
selected well-seasoned stock. The usual method of treatment is to 
paint them with white lead and oil. The size of cross-arms and 
spacing of pins have not been thoroughly standardized. For cir¬ 
cuits up to 5,000 volts, 3|- by 4§-inch cross-arms with spacing between 
pins of 12 or 14§ inches, and the pole pins spaced 22 inches, are recom¬ 
mended. For higher voltages, special cross-arms and spacings 
are necessary. The cross-arms should be spaced at least 24 inches 
between centers, the top arm being placed 12 inches below the top 
of the pole. They are usually attached to the pole by means of two 
bolts and are braced by galvanized iron braces not less than 1J by 
t 3 ^ inch and about 28 inches long. 

Cross-arms are placed on alternate sides of the poles so as to 
prevent several of them from being pulled off should one become 
broken or detached. On corners or curves, double arms are used. 
In European practice, the cross-arm is done away with to a large 
extent, the wire being mounted on insulators attached to iron 
brackets mounted one above the other. 

The distance between conductors for aerial lines is governed 
by the voltage of v the system and the distance between supports. 
For ordinary work the average figures are about as follows: 

From 2,300 to 6,600 volts, 2 feet 4 inches 
From 10,000 to 20,000 volts, 3 feet 4 inches 
From 20,000 to 30,000 volts, 4 feet 0 inches 
From 30,000 to 50,000 volts, 5 feet 0 inches 
From 50,000 to 60,000 volts, 6 feet 0 inches 

Insulators. Electrical leakage between wires must be pre¬ 
vented in some way and various forms of insulators are depended 
upon for this purpose. The material used in the construction of these 
insulators should possess the following properties: (a) high specific 
resistance; (b) surface not readily destroyed and one on which mois¬ 
ture does not readily collect; (c) mechanical strength to resist both 
strain and vibrating shocks. Its design must be such that the wire 
can readily be fastened to it and the tension of the wire be transmit¬ 
ted to the pin without producing an excessive strain in the insulator. 
Leakage surface must be ample for the voltage of the line and so 
constructed that a large portion of it will be protected from mois- 


64 


POWER TRANSMISSION 


ture during rainstorms. The principal materials used are glass 
and porcelain. 

Porcelain has the advantage over glass in that it is less brittle 
and generally stronger and is less hygroscopic, that is, moisture 
does not so readily collect on and adhere to its surface. Glass is 
less conspicuous and is cheaper for the smaller insulators. Both 
materials are freely used for the construction of high-tension lines, 
while the use of glass prevails for the low-tension circuits. 



Fig. 40. Suspended or Disk Type of Insulator 


Many line insulators are of the petticoat type and are made up 
in various shapes and sizes. The larger size porcelain insulators are 
made up in two or more pieces which are fastened together by means 
of a paste formed of litharge and glycerin. The advantages of 
this form of construction are greater uniformity of structure, and 
that each part may be tested separately. 

For the higher potentials—voltages from 60,000 to 110,000—a 
suspended or dish type of insulator is now in use, its construction 
being shown in Fig. 40. The advantages of this insulator are: (1) 










POWER TRANSMISSION 


65 


HE/GHT 3+ 
TESTED AT sqoook 




HE/GHT 3 

TESTED AT 30,000If 



/ " 

HE/GHT At* 
TESTED AT 70,000 V. 



TESTED AT <30.0001C 



HE/GHT H6 

Tested at so.ooo vf 



TESTED AT 30,000 If 



HE/GHT 3^ 
TESTED AT 4-0,000 V 



HE/GHT H-5- 


TESTED AT HQ,OOOK 


Fig. 41. Types of Petticoat Insulators 









































66 


POWER TRANSMISSION 


/DIAMETER 
CC/T ECCENTRIC//I 
BOLT CUTTER 


■Is DIAMETER 
+M/LD STEEL 


by using the proper number of disks in series, the higher line potentials 
become practical; (2) the material is subjected to compressive strains 
only; and (3) there is likelihood of less torsional strain on the cross- 
arms. A slight additional height of pole is necessary and the line 
wires must be anchored at intervals to prevent excessive swaying. 

Fig. 41 shows several forms of 
petticoat insulators now in use 
with the voltage at which they 
are tested. The test applied to 
an insulator for high-tension lines 
should be at least double the volt¬ 
age of the line, and some engineers 
recommend three times the nor¬ 
mal voltage. 

Pins. Pins made of locust 
wood boiled in linseed oil are 
preferred for voltages up to 5,000. 
Above this, special pins are used. 
Wood pins are often objected to 
on account of the burning or char¬ 
ring which takes place in certain 
localities. Iron pins are now be¬ 
ing used to a large extent. The 
dimensions of such a pin used on 
a 60,000-volt line are given in 
Fig. 42. Other forms of pins are 
shown in Fig. 43. The insulator 
is fastened to the pin by means 
of a thread in a lead lug which is cast on top of the pin. The in¬ 
sulators in the construction shown in Fig. 42 are cemented to the 
iron brackets. 

Line Stresses. The stresses sustained by the line may be classi¬ 
fied as follows: 



CAST IRON Ere DIAMETER 

Fig. 42. Iron Pin Showing Dimensions 


1. Weight of wire, which includes insulation, and snow and sleet which 
may be supported by the wire. 

2. Wind pressure upon the parts of the line. 

3. Tension in the wire itself. 

Weight of Wire. The strain produced by the weight of the wire 
on the pole itself need not be considered except in exceptional cases. 



































POWER TRANSMISSION 


67 


because if the pole is sufficiently strong to withstand the bending 
strains, it is more than strong enough to withstand the compression. 

Wind Pressure. Langley shows the pressure of the wind normal 
to flat surfaces to be equal to 

p= .0036 

where p is pressure in pounds per square feet and v is velocity in 
miles per hour. 

For cylindrical surfaces the amount of pressure is two-thirds of 
that exerted on a flat surface of a width equal to the diameter of the 
cylinder. Without great error we may assume that the maximum 
wind pressure, and that for which calculation is necessary, is that 
at right angles to the line, and a value of thirty pounds per square 



Fig. 43. Forms of Pins. Cross-Arm 2300-6600 Volts; Pole-Top 2300-6600 Volts; 
Cross-Arm 10,000-30,000 Volts; Pole-Top 10,000-30,000 Volts 


foot is sufficient allowance for exposed places, while twenty pounds 
per square foot is sufficient for lines partially sheltered. 

Example. What is the pressure, due to the wind, on the wires 
of a pole line containing three No. 0000 wires, the poles being 
spaced 45 yards and the velocity of the wind such that the pressure 
may be taken at 30 pounds per square foot? 

The diameter of a No. 0000 wire is .460 inch. The area against 
which the wind exerts its force may be considered as 

2 3 X 45 X 3 X 12 X .460 

— X-—- = 10.35 square feet 

3 144 

10.35X30=310.5 pounds 










68 


POWER TRANSMISSION 


Tension. The most important strain-producing factor in a line 
is that due to the tension in the wire itself. A wire suspended so as 
to hang freely between two supports assumes the form of curve 
known as a catenary , but for ordinary work the curve may be taken 
as a parabola , the equation of which is simple and from which the 
following equations are derived: 

HW 


_HW 
>6 “ 8D 


L = H+ 


8D 2 
3 H 


When D is deflection or sag at lowest point in feet; L is actual length 
of wire between supports in feet; H is distance between supports in 
feet; W is weight of wire in pounds per foot: and P o is horizontal 
tension in the wire at the middle point. 


T 

n 


where T is tensile strength of the wire and n is factor of safety; 
n— 2 to 6 under the conditions existing when the wire is erected. 
The temperature changes in the wire affect the value of this factor, 
it being a maximum when the temperature is the greatest, and a 
minimum when the temperature is the lowest, and calculation should 
be for the maximum strain that may come on the wires. 

if L t is length of a wire at a given temperature, t° F., and L 20 
is length of a wire at a given temperature, 20° F., then 

L t = L w { l“h& 0—20)] 

Values of h per degree Fahrenheit for materials used for line 
wires are given as follows: 

Steel.0.0000064 

Aluminum.0.0000128 

Copper.0.0000096 

On account of the fact that the conductor is elastic, the full 







POWER TRANSMISSION 


09 


TABLE IX 

Temperature Effects in Spans 


Spans 

in 

Feet 

Temperature in Degrees Fahrenheit 

-10° 

30° 

40° 

50° 

60° 

70° 

oo 

o 

90° 

100° 

Deflection in Inches 

50 

.5 

6 

8 

9 

9 

10 

11 

11 

12 

60 

.7 

8 

10 

11 

11 

12 

13 

13 

14 

70 

1 . 

10 

11 

12 

13 

14 

15 

15 

17 

80 

1.2 

11 

13 

14 

15 

16 

17 

18 

19 

90 

1.6 

13 

14 

16 

17 

18 

19 

20 

21 

100 

1.9 

14 

16 

17 

19 

20 

21 

23 

24 

110 

2.3 

16 

18 

19 

21 

22 

24 

25 

26 

120 

2.8 

17 

19 

21 

22 

24 

26 

27 

28 

140 

3.7 

20 

23 

25 

27 

28 

30 

32 

33 

160 

4.9 

23 

26 

28 

30 

32 

34 

36 

38 

180 

6.2 

26 

29 

32 

34 

37 

39 

41 

43 

200 

7.7 

31 

33 

36 

38 

41 

43 

45 

48 


value of k as given above does not apply, as with higher tempera¬ 
tures the strain on the wire is reduced and the elasticity of the 
material reduces the actual length of wire between supports. On 
this account the values to be used in line calculations should be about 
one-third those given above for copper and aluminum and one-half 
the above value for steel. 

Example. A galvanized steel wire having a tensile strength of 
45,000 pounds per square inch and weighing 330 pounds per mile 
is strung on poles spaced 35 to the mile. It is so strung that at 0° F. 
the actual length of wire between supports is 150.80754 feet. What 
will be the length of wire between supports when the temperature 
is raised to 80° F.? 

Use for k a value equal to \ of 0.0000064, or 0.0000032. Then 
L— 150.80754 (1+0.0000032X80) 

= 150.80754X 1.000256= 150.846 feet 

Ans. 150.846 feet. 

Table IX gives the deflection of spans of wire in inches for differ¬ 
ent temperatures and different distances between poles, a maximum 
stress of 30,000 pounds per square inch being allowed at —10° F., 
which gives a factor of safety of 2 for hard-drawn copper wire. 























70 


POWER TRANSMISSION 


The above formulas apply directly to lines in which the poles 
are the same distance apart and on the same level, and any number 
of spans may be adjusted at one time by applying the calculated 
stress at the end of the wire, and the line will be in equilibrium, 
that is, there will be no strain on the poles in the direction of the 
wires. Special care must be taken to preserve this equilibrium when 
the length of span changes or when the level of the pole tops varies, 
and this is accomplished by keeping P c and n constant for every span. 

Example. What is the tension in pounds per square inch at the 
center of a span of No. 0000 wire, when the poles are 120 feet apart 
and the sag is 16 inches? 

WW 

P = - 

c 8D 

II = 120 
1( 5 

D = —= 1J feet 


P = 


W = .64 pounds 
(120) 2 X .64 


8 X 1J 


= 864 pounds 


The cross-section of No. 0000 wire is 

n X (.23) 2 = .1662 square inches 
864 -T- .1662 = 5,200 pounds per square inch 

By making use of the modulus of elasticity* of tne material 
employed for the line, the actual length of the conductor under 
different strains may be determined and from this elongation the 
length of the wire, if not subjected to stress, may be found. With 
the length of the conductor, when not subjected to stress, known, 
the length of the unstressed conductor at any different temperature 
may be determined by using the true coefficient of expansion in the 
formula already given. As the temperature changes, the sag and 
the strain on the conductor both change, and the wire will, of course, 
take up such a position that the strain due to the weight of the wire 
and the wind will ju?t be balanced by the strain due to its elasticity. 

If E equals the elongation of the conductor due to stress, M 
equals the modulus of elasticity, and a equals the area, then 

♦Modulus of elasticity is defined as the stress required to stretch a bar to twice its original 
length, assuming the material to remain perfectly clastic. 





POWER TRANSMISSION 


71 


E = 


p Jl 

Mu 


For the different materials used in line construction M may 
be taken as follows: 


Aluminum. 9,000,000 

Copper, hard drawn.16,000,000 

Steel.27,000,000 


The calculation of a line in which use is made of the modulus of 
elasticity of the material and the true coefficient of expansion is given 
in the following example. 

Example. Find the deflection and the length of the cable as 
strung when at —20° F. and stressed to the elastic limit, when the 
distance between supports equals 1,000 feet; the conductor is a 500,000 
circular mil aluminum cable; the area is .393 square inch; weight 
is .46 pound per foot; the elastic limit of wire is 5,500 pounds; and 
the modulus of elasticity is 9,000,000. 

Assume a wind pressure such that the resultant of the wind and 
the weight of the conductor amount to .85 pound per foot, and 
that at —20° F., the cable is stressed to the elastic limit. What 
will be the deflection and the tension on the cable when the line 
temperature is raised 130° F.? 


D = 


1,000 2 X .85 
8 X 5,500 


= 19.3 feet 


L = 


1 , 000 -*- 


8 X 19.3 2 
3,000 


= 1,000.992 feet 


5,500 X 1,000.992 
9,000,000 X .393 


.56 feet 


Length of conductor unstressed equals 

1,000.992-1.56, equals 999.432 feet 

Length of conductor unstressed at 130° F. equals 

999.432 (1+150X .0000128), equals 
1,001.352 feet. This would correspond to 
a deflection of 22.5 feet. 








72 


POWER TRANSMISSION 


When the cable is stressed as it is when supported at points 
1,000 feet apart, the cable will sag more than 22.5 feet and the 
simplest manner of finding this deflection and the resultant tension 
is to assume different tensions in the wire and calculate the deflec¬ 
tions from the equation 



and plot the values in a curve AB, Fig. 44. Next calculate, from 



Fig. 44. Graphical Solution of Example, Page 71 

the formula, the increase in the length of the conductor for each 
deflection, using the modulus of elasticity, and obtain the deflection 

and plot the curve CD, Fig. 44. The point where these two curves 
cross gives the resultant deflection and tension. 

Ans. Deflection, 27 feet; Tension, 2,150 pounds. 


















































POWER TRANSMISSION 


The regulation of the system and the amount of power lost in 
transmission together determine the cross-section of the conductors 
to be used. The amount of power lost, for most economical opera¬ 
tion, can be determined from the cost of generating power and the 
fixed charges on the line investment. 

Conductors. The most economical conductor to use is the 
one which makes the sum of the annual charges for line and the 
annual charges for energy lost in the line a minimum. In general, 
it can best be determined by assuming about three sizes of con¬ 
ductor and calculating the total annual charges for each size, select¬ 
ing the most economical one for the construction. Total annual 
charges can be determined only when all local conditions are known. 
Usually the loss of power will not exceed 10 per cent of the amount 
delivered. Either copper or aluminum wire or cables may be used 
although copper is the more common. Aluminum is lighter in 
weight than copper, but more care is necessary in erecting it and 
it is more difficult to make joints, 

UNDERGROUND CONSTRUCTION 

In large cities or other localities where, if overhead construc¬ 
tion be used, the number of conductors becomes so great as to be 
objectionable, not alone on account of appearance but also on 
account of complication and danger, the lines are run underground. 
The expense of installing underground systems is very great com¬ 
pared with that of overhead construction, but the cost of mainte¬ 
nance is much less and the liability to interruption of service, due 
to line troubles, is 'greatly reduced. The essential elements of an 
underground system are the conductor, the insulator, and the pro¬ 
tection. The conductor is invariably of copper, the insulator may 
be rubber, paper, some insulating compound, or individual insu¬ 
lators, depending on the system, while the protection takes one of 
several forms. 

Systems. The system, as a whole, may be divided into (a) 
solid, or built-in, systems; (b) trench systems; and (c) drawing-in 
systems. 

Solid , or Built-In. As an example of the solid, or built-in, system, 
we have the Edison tube system, which is especially adapted to house- 


74 


POWER TRANSMISSION 


1 


2 




3 4 

Fig. 45. Coupling Boxes Used in Edison Tube System 





POWER TRANSMISSION 


75 


to-house distribution and is used to some extent for direct-current 
three-wire distribution in congested districts. It is made up of copper 
rods as conductors—three of equal size for mains and the neutral 
but one-half the size of the main conductors in feeders—which are 
insulated from each other by an asphaltum compound. This com¬ 
pound also serves as an insulation from the protecting case, which 
consists of wrought-iron pipe. Pilot wires are also often installed in the 
feeder tubes. This tube is built up in sections about 20 feet long. 
In insulating the conductors, they are first loosely wrapped with 
jute rope so as to keep them from making contact with each other 
and with the pipes, and the heated asphaltum forced into the tube 
from the bottom, when the tube is in a vertical position. The 
ends of the conductors and the tubes must be joined and properly 
insulated in a completed system. Special connectors are furnished 
for the conductors, and cast-iron coupling boxes are fitted to the 
ends of the tube, as shown in Fig. 45. After the conductors are 
properly connected, the cap is put on this coupling box and the 
inside space then filled with insulating compound through a hole 
in the cap. This hole is later fitted with a plug to render the box 
air-tight. The system is a cheap one, though the joints are expen¬ 
sive. It is not adapted to high potentials. 

The Siemens-Halske system of iron-taped cables consists of 
insulated cables encased in lead to keep out moisture, this lead 
sheathing being in turn wrapped with jute which forms a bedding 
for the iron tape. The iron tape is further protected by a wrap¬ 
ping thoroughly saturated with asphaltum compound. These 
cables may be made up in lengths of from 500 to 600 feet. 

In unexposed places, such as across private lands, the steel 
taping may be omitted and the lead sheathing simply protected by 
a braid or wrapping saturated with asphaltum. 

Trench System. The trench system consists of bare or insulated 
conductors supported on special forms of insulators as in overhead 
construction, the whole being installed in small closed trenches. 
This system is not used to any extent in America. 

In the Crompton trench system, bare copper strips are used, each 
1 to \\ inches wide and J to \ inch thick. These strips rest in notches 
on the top of porcelain or glass insulators, supported by oak tim¬ 
bers which are embedded in the sides of a cement-lined trench. 


76 


POWER TRANSMISSION 


This trench is covered with a layer of flagstone. The insulators 
are spaced about 50 feet, and about every 300 feet a straining device 
is installed for taking up the sag in the conductors. Handholes 
are located over each insulator. 

Drawing-In Systems. There are a number of drawing-in sys¬ 
tems, of which several have come to be considered standard under¬ 
ground construction in the United States. It is no longer deemed 
advisable to construct ducts which will serve as insulators, but they 
are depended on for mechanical protection only, and should fulfil 
the following requirements: 

They must have a smooth interior, free from projections, so that the 
cables may readily be drawn in and out. 

They must be reasonably water-tight. 

They must be strong enough to resist injury due to street traffic and ac¬ 
cidental interference from workmen. 

Conduit Materials. Among the materials used for duct con¬ 
struction are iron or steel, wood, cement, and terra cotta. 

Wood. Wood is used in the form of a trough or box, or in the 
form of wooden pipes. The latter is known as pump log conduit. 
The wood used for this purpose must be very carefully seasoned 
and then treated with some antiseptic compound, such as creosote, 
in order that the duct may give satisfactory service. If improperly 
treated, acetic acid is formed during the decay of the wood, and this 
attacks the lead covering of the cable, destroying it and allowing 
moisture to deteriorate the insulation. Wood offers very little 
resistance to the drawing in of the cables, and it is a cheap form of 
conduit, though it cannot be depended on for long life. 

Wrought Iron. One of the best and at the same time most expen¬ 
sive systems is the one using wrought-iron pipes, laid in a bed of con¬ 
crete. The ordinary construction of the duct consists of digging a 
trench of the desired size and covering the bottom, after it is carefully 
graded, with a layer of good concrete from 2 to 4 inches thick. Such 
a concrete may consist of Rosendale cement, sand, and broken stone 
in the ratio of 2:3:5, the broken stone to pass through a sieve of 
1^-inch mesh. The sides of the trench are lined with 1 J-inch planks. 
The first layer of pipes, consisting of wrought-iron pipes 3 to 4 
inches in diameter, 20 feet long, and \ inch thick, joined by means 
of water-tight couplings, is laid on this concrete, and the space around 


POWER TRANSMISSION 


77 


and above them filled with concrete. A second layer of pipes is 
laid over this, and so on. A covering of concrete 2 to 3 inches thick 
is placed over the last layer, and a layer of 2-inch plank is placed 
over all, to protect against injury by workmen. Fig. 46 shows a 
cross-section of such duct construction. The pipe should be reamed 
so as to remove any internal burs which might injure the insulation 
during the process of drawing in. 

A modification of this system consists of the use of cement- 
lined wrought-iron pipes, of 8-foot lengths made of riveted sheet- 
iron pipes. Rosendale cement is used for the lining, which is about 
f inch thick. The external diameter of the pipe is about inches. 
The outside of the pipe is coated with tar to prevent rusting. The 



sections have a very smooth interior and are light enough to be easily 
handled. They are embedded in concrete, similar to the system 
previously described. Connections between the sections are made 
by means of joints, constructed on the ball-and-socket principle, 
moulded in the cement at the ends of the sections. This forms a 
cheaper construction than the use of full-weight pipe. 

Earthemcare. This form of conduit is being extensively used 
for underground cables. The sections may be of either the single- 
















78 


POWER TRANSMISSION 


duct or multiple-duct type. The former consists of an earthenware 
pipe from 18 to 24 inches in length with internal diameter from 2§ 
to 3 inches. These are laid on a bed of concrete, the separate tiles 
being laid up in concrete in such a manner as to break joints between 
the various ducts. In the multiple-duct system the joints are wrapped 
with burlap and the whole embedded in concrete. This form of con¬ 
duit has a smooth interior and the cables are readily drawn in and 
out. The single-duct type lends itself admirably to slight changes 
of direction that may be necessary. Fig. 47 shows both forms of 
duct, while Fig. 48 shows a cement-lined iron-pipe duct system, 
laid in concrete, in course of construction. 

Other forms of conduits are ducts formed in concrete, earthen¬ 
ware troughs, cast-iron troughs, cement pipe, and fiber tubes, 




.Fig. 47. Single- and Multiple-Duct Tile Conduits 


Manholes. For all drawing-in systems, it is necessary to pro¬ 
vide some means of making connections between the several lengths 
of cable after they are drawn in, as well as for attaching feeders. 
Since the cables cannot be handled in lengths greater than about 
500 feet, and less than this in many cases, vaults or junction boxes 
must be placed at frequent intervals. Such vaults are known as 
splicing vaults or manholes. The size of the manhole depends upon 
the number of ducts in the system, as well as on the depth of the 
conduit. If the ducts be laid but a short distance from the surface 
of the street and traffic is light, the cables may readily be spliced with 




POWER TRANSMISSION 


79 


a manhole but 4 feet square and 4 feet. deep. The smaller vaults 
are often called handholes. Deeper vaults are from 5 to 6 feet square, 
and the floor should be at least 18 inches below the lowest ducts 
on account of convenience to the workmen and to serve as collect¬ 
ing basins for water which gets into the system. The ducts should 
always be laid with a gentle slope toward such manholes. 

Common construction consists of a brick wall laid upon a con¬ 
crete floor, the brick being laid in cement and being coated inter¬ 
nally with cement. The cables follow the sides of the manhole 
and they are supported on hooks set in the brickwork. This causes 



Fig. 48. Cement-Lined, Iron-Pipe Duct System in Course of Construction 


quite a waste of cable in large manholes. Care should be taken that 
workmen do not use the cables, so supported, as ladders in entering 
and leaving the manhole, as the lead sheathing may readily be 
injured when the cables are so used. 

Conductors are drawn into place by the aid of some form of 
windlass. Special jointed rods, 3 to 4 feet long, may be used for 
making the first connection between manholes or a steel wire or tape 
may be pushed through. A rope is drawn into the duct and the 




80 


POWER TRANSMISSION 


cablp is attached to this rope. Fig. 49 shows one way in which the 
cable may be attached to the rope. Care must be taken to see that 
no sharp bends are made in the cable during this process. Cable 
should not be drawn in during extremely cold weather unless some 
means is employed for keeping it warm, owing to the liability of 
the insulation to be injured by cracking. 

Conduit systems must be ventilated in order to prevent ex¬ 
plosion due to the collecting of explosive mixtures of gas. Many 
special ventilating schemes have been tried, but the majority of 
systems depend for their ventilation on lvdes in the manhole covers. 
This prevents excessive amounts of gas from collecting but does 
not always free the system from gas so comoletely as to make it 


LEAD 



Fig. 49. Tackle for Fastening Cable to Rope to Draw Cable 
Through Ducts 


safe for workmen to enter the splicing vault until the impure air has 
been pumped out. 

Auxiliary ducts are laid over the main ducts and distribution 
is accomplished from handholes. 

It is customary to ground the lead sheaths of the cables at 
frequent intervals, thus in no way depending pn thp ducts, even 
when made of insulating material, for insulation. 

Cables. Well-insulated copper cables are used for under¬ 
ground systems. On account of the fact that various materials, 
such as acids and oils which are injurious to the insulation, come 
in contact with the cable, it is necessary that it be protected in 
some manner. A lead sheath is employed for this purpose. This 
sheath is made continuous for the whole length of the conductor, 
and with its use it is possible to employ insulating materials such 
as paper which, on account of being readily saturated by moisture, 
could not be used at all without such a hermetically sealed sheath. 
Lead containing a small percentage of tin is usually employed for 










POWER TRANSMISSION 


81 


this purpose. The sheath may consist of a lead pipe into which 
the cable is drawn, after which the whole is drawn through suitable 
dies, bringing the lead in close contact with the insulation, or the 
casing may be formed by means of a hydraulic press. 

Yarns thoroughly dried and then saturated with such materials 
as paraffin, asphaltum, rosin, etc., paper, both dry and saturated, 
rubber, and varnished cambric are the materials generally employed 
for insulation. When paper is employed, it is wound on in strips, 
the cable being passed through a die after each layer is applied, after 
which it is dried at a tem¬ 
perature of 200° F. in order 
to expel moisture. After 
being immersed in a bath 
of the saturating compound 
it is taken to the hydraulic 
presses where the lead 
sheath is put on. 

Varnished cambric in¬ 
sulation consists of strips of 
varnished cloth treated with 
insulating varnish and ap¬ 
plied much the same as paper insulation. Where the cable is not 
exposed to moisture, as in a great deal of power plant wiring, no 
lead sheath is needed with varnished cambric insulation but the lead 
sheath is required for underground conduit work. 

When rubber insulation is used, the conductors are tinned to 
prevent the action of any uncombined sulphur which may be present 
in the vulcanized rubber. The Hooper process consists of using 
a layer of pure rubber next to the conductors and using the vulcanized 
rubber outside of this. One or two layers of pure rubber tape are 
put on spirally, the spiral being reversed for each layer. Rubber 
compound in two or more layers is applied over this in the form of 
two strips which pass between rollers which fold these strips around 
the core and press the edges together. Prepared rubber tape is 
applied over this, after which the insulator is vulcanized and the 
cable tested. If satisfactory the external protection is applied. 

Cable for polyphase work is made up of three conductors in 
one sheath, Fig. 50 shows a cross-section of cable manufactured for 



82 


POWER- TRANSMISSION 


TABLE X 

Typical Cable Construction 


Cables 

No. of Conductors 

^Character 

of 

Conductor 

Sizes of 
Individual 
Wires 

Electric light less than 500 
volts. 

Single 

Stranded 

No. 10B.&S. 
or smaller 

Arc lighting. 

Single 

Solid 

No. 6 or 4 

B. & S. 

High-tension power transmis¬ 
sion ... 

Single, concentric, 
duplex, or three 
conductors 

Stranded 

No.lOB.&S. 
or smaller 


Thickness of Insulation 



Rubber 

Saturated 

Fiber 

Saturated 

Paper 

Dry 

Paper 

Thickness 
of Lead 


Inch. 

Inch. 

Inch. 

Inch. 

Inch. 

Electric light less than 500 






volts. 

A 

A 

A 

A 

A to 

Arc lighting.. . . . . 

A to fa 

A 

A 

A 

tV 

High-tension power trans¬ 






mission . 

A to fa 

A 

A 

A 

A 


three-phase transmission at 6,600 volts. The conductors of this 
cable have a cross-section equivalent to a No. 0000 wire, to which 
an insulation of rubber inch thick is applied. These three con¬ 
ductors are twisted together with a lay of about 20 inches. Jute 
is used'as a filler, and a second layer of rubber insulation inch 
thick is then applied. The lead sheath employed is J inch thick, 
and is alloyed with 3 per cent of tin. 

Joints in cables must be carefully made. Well-trained men- 
only should be employed. The insulation applied to the joint should 
be equivalent to the insulation of the cable at other points, and 
the joint as a whole must be protected by a lead sheath made continu¬ 
ous with the main covering by means of plumbers’ joints. 

Some engineers prefer rubber, some prefer paper or varnished 
cambric insulation, but all types are giving good service, and are 
used up to voltages of 22,000. It is customary to subject each cable 
to twice its normal potential soon after it is installed. This voltage 
should not be applied or removed too suddenly, as unnecessary 
strains might be produced in this manner. 
























POWER TRANSMISSION 


83 


Rubber-insulated cables should never be allowed to reach a 
temperature exceeding 65° to 70° C. (149° to 158° F.). Paper will 
stand a temperature of 90° C. (194° F.), but it is neither desirable 
nor economical to allow such a temperature to be reached. Var¬ 
nished cambric insulation can be run at a temperature of 100° C. 
without injury. It is less expensive than rubber, but costs more than 
paper. Table X is of interest in connection with underground cables. 
The dimensions here given are only general. 

MISCELLANEOUS FACTORS 

Selection of Voltage. The voltage to be selected for a given 
system depends on the distance the power is to be transmitted as 
well as its amount, and on the use to be made of the power. If a 
lighting load is concentrated in a small district, a 220-volt three- 
wire system will give very good service. If the region is a little 
more extended, possibly a 440-volt three-wire system using 220- 
volt lamps would serve the purpose without an excessive loss of 
power or a prohibitive outlay for copper. For location when the 
service is scattered, a distribution at from 2,200 to 4,000 volts alter¬ 
nating current is used, transformers being located as required for 
stepping down the voltage for the units which may be fed from a two- 
or three-wire secondary system. 

2,300 volts (alternating) is a standard voltage for lighting 
purposes and for polyphase systems; 2,300 volts is often taken as 
the voltage between the outside wires and the neutral wire of a four- 
wire three-phase distribution. 

For railway work, 550 to 600 volts direct current is used up 
to distances of about 5 or 6 miles, beyond which it becomes more 
economical to install an alternating-current main station and supply 
the line at intervals from substations to which the power is trans¬ 
mitted at voltages of from 6,600 to 30,000 or even higher, depend¬ 
ing on the distance it is to be transmitted. At present, the highest 
voltage used in long-distance transmission is 110,000, and even 
higher values are contemplated. Such voltages are used only on 
very long lines, and each one becomes a special problem. It is 
always well to select a voltage for apparatus which may be con¬ 
sidered as standard by manufacturing companies, as standard ap¬ 
paratus may always be purchased more cheaply and furnished in 


84 


POWER TRANSMISSION 


shorter time than special machinery. The following voltages are 
now considered standard for transmission purposes: 6,600, 11,000, 
22,000, 33,000, 44,000, 66,000, 88,000, and 110,000. 

Line Protection. Lightning arresters are installed at intervals 
along overhead lines for the protection of connected apparatus. 
For ordinary lighting circuits, such arresters are installed for the 
protection of transformers, and are located preferably on the first 
pole away from the one on which the transformer is installed. Care 
should be taken to see that there are no sharp bends or turns in the 
ground wire and that there is a good ground connection. For the 
high-tension lines, lightning arresters at either end of the circuit 
are relied on to afford the greater part of the protection. In some 
localities, a wire strung on the same pole line at a short distance 
from the power wires and grounded at very frequent intervals has 
been found to reduce troubles due to lightning. 

The grounding of the neutral of three-wire secondary systems 
forms a means of protection of such circuits against high potentials 
which might arise from accidental contact with the primaries, and 
is recommended in some cases. The grounding of the neutral of 
high-tension systems reduces the potential between the lines and 
the ground, but a single ground will cause a short-circuit on the 
line with any grounded system. Grounding, through a resistance 
which will limit the flow of current in such a short-circuit, has been 
recommended and is employed in some instances. Spark arresters 
are installed at the ends of high-tension underground systems to 
prevent high voltages which might injure the insulation in case of 
sudden changes in load, grounds, and short-circuits. 


INDEX 


A 

PART 


Air-cooled transformers. I, 

Alternating-current lines. II, 


B 


Boilers. 

classification. 

economic. 

fire-tube. 

Galloway. 

multitubular. 

water-tube. 

deterioration. 

draft. 

mechanical. 

natural. 

efficieiicy. 

feed water. 

feeding appliances. 

firing of. 

floor s£>ace. 

initial cost. 

setting.. 

steam piping.- ,. 

superheated steam.-,:. 

Buildings.. 

foundations. ,. 

methods of charging for power. . . 

station arrangement. 

station records. 


i, 

i, 

i, 

i, 

i, 

i, 

i, 

i, 

i, 

i, 

i, 

i, 


i, 

i, 

i, 

i, 

i, 

i, 

i, 

i, 

1: 

I, 


c 


cables..,,..:. II, 

Conductors. II, 

current-carrying capacity. II, 

insulation. II, 

material. II, 

resistance. II, 

Conduit materials. II, 

Cfoss-arms.-... II, 


PAGE 

43 

35 


8 

9 

10 

9 

10 

10 

10 

11 

22 

23 

22 

11 

19 

20 
23 
11 
11 
22 
13 
18 
72 
74 
86 

78 

79 


80 
1, 73 

7 

8 
1 
3 

76 

63 






































2 


INDEX 


D 

PART PAGE 

Distribution systems (alternating current). II, 22 

amount of copper for different systems. II, 28 

parallel. II, 23 

polyphase. II, 27 

series. II, 22 

voltage regulation. II, 23 

Distribution systems (multiple circuit). II, 18 

three-wire. II, 18 

voltage regulation. II, 21 

Distribution systems (single circuit). II, 11 

parallel. II, 13 

series. II, 11 

series-multiple and multiple-series. II, 18 

E 

Economic boiler. I,' 10 

Electric plant. I, 38 

excitation. I, 41 

generators. I, 38 

speed and regulation. I, 42 

F 

Feed water. I, 19 

Feeding appliances. I, 20 

Fire-tube boilers. I, 9 

Firing of boilers. I, 23 

stoking. I, 24 

G 

Galloway boiler. I, 10 

Gas plant. I, 36 

Generators. I, 38 

capacity. I, 39 

efficiency. I, 40 

mechanical features. I, 42 

air-cooled transformers. I, 43 

oil-cooled transformers. I, 44 

storage batteries. I, 46 

water-cooled transformers. I, 45 

types. I, 39 

H 

Hydraulic plants. I, 31 

I 

Insulators. II, 63 






































INDEX 3 

L 

PART PAGE 

Line protection. u 84 

Line stresses. n, 60 


M 

Manholes. H, 78 

Multitubular boiler. I, io 


0 

Oil-cooled transformers. I, 44 

Oil switches. I, 57 

Overhead lines. II, 56 

conductors. II, 73 

cross-arms. II, 63 

insulators. II, 63 

line stresses. II, 66 

location of line. II, 57 

pins. II, 66 

poles. II, 58 


P 

Panels. I, 49 . 

Pins. II, 66 

Plants, design of. I,. 7 

Poles. II, 58 

Power stations. I, 1-86 

buildings. I, 72 

electric plant. I, 38 

gas plant. I, 36 

general features. I, 4 

hydraulic plants. I, 31 

location of. I, 2 

steam plant. I, 8 

substations. I, 68 

switchboards. I, 47 

Power transmission. II, 1-84 

conductors. II, 1 

distribution systems. II, 11 

miscellaneous factors. II, 83 

overhead lines. II, 50 

transformers. II, 49 

transmission lines. II, 29 

underground construction. II, 73 






































4 


INDEX 


S 


Safety devices. 

Station, location of. 

accessibility. 

cost of real estate. 

facility for extension.. . 
stability of foundations, 

surroundings. 

water supply. 

Station arrangement. 

Station records. 

Steam engines. 

Steam piping. 

arrangement......... 

expansion. 

fittings.- ... .. 

lagging. . . .. 

location. 

loss in pressure. 

material. 

mounting. 

size. : . . 

Steam plant. 

boilers. 

engines. 

turbines. 

Steam turbines. 

advantages. 

types. 

Storage batteries. 

Substations. 

Superheated steam. 

Switchboards. 

oil switches. 

panels. 

safety devices. 


T 


Table 

aluminum Wire, pure. . . i 

boiler efficiencies. 4 4 ; .-.-.-.- 

boiler floor space. .-.-.-.-.-.- ; .- ; ; 

cable construction^ typical. ... 
capacity ratios. . ; 

conductors, class of for various positions, 

conductors for various conditions. 

copper, temperature coefficients for. .... 
copper wire.. 


I, 

I, 

I, 

I, 

I, 

I, 

I, 

If 

I, 

I, 

I, 

1 : 

1 , 

I, 

1 

5 ; 

I, 

I, 

I. 

I, 

I, 

I, 

I, 

i: 

ij 

I, 

I, 

i, 


Hi 

i, 

i, 

n, 

h 

ii, 
ii, 

ii, 

ii, 


61 

2 

2 

3 

3 

3 

3 

2 

78 

79 
24 

13 

14 
17 

17 

18 
18 
17 

15 
17 

17 
8 
8 

24 

26 

26 

26 

27 

46 
68 

18 

47 
57 
4b 
61 


4 

12 , 19 
11 
82 
71 
10 
10 

5 
2 




















































INDEX 


5 


Table PART PAGB 

exciters for single-phase alternating-current gen¬ 
erators. I, 41 

full load ratios. I, 71 

horsepower per cubic foot of water per minute for 

different heads. I, 36 

inductance per mile of three-phase circuit. II, 32 

maximum efficiencies, average. I, 40 

permissible overload 33 per cent. I, 8 

power plants, thickness of walls for. I, 74 

riveted hydraulic pipe. I, 34 

spans, temperature effects in. II, 69 

standard wire. I, 50 

three-phase system, capacity in microfarads per 

mile of circuit for. II, 31 

water, pressure of. I, 33 

water, rate of flow of I, 21 

wires, safe-carrying capacity of. II, 6 

Transformers. 1,42; II, 49 

choice of frequency. II, 55 

connections. II, 53 

efficiency. II, 50 

power losses. .. II, 50 

regulation. II, 52 

Transmission lines.. II, 29 

alternating-current lines. II, 35 

capacity. II, 29 

inductance. II, 30 

U 

Underground construction. II, 73 

cables. II> 80 

conduit materials. II, 76 

manholes. H» 78 

systems. II, 73 

Y 

Voltage. H> S3 

W 

Water-cooled transformers. I, 45 

Water-tube boilers. I> 10 

Water turbines. I> 32 






































































* 


' 





. 








The School Behind the Book 


T HIS practical handbook is one of the representatives of 
the American School of Correspondence. It is the only 
kind of representative by which the School reaches the 
general public and extends its educational work. 

The American School of Correspondence is chartered, under 
the same laws as a State University, as an educational institution. 
Its instruction books, written especially to suit the needs of men 
seeking self-improvement through correspondence work, are 
reserved for its students and for class use in educational institu¬ 
tions; many of these texts are used in the class room work of the 
best resident schools in the country. 

However, in order that the large number of ambitious men, 
for whom class work and correspondence study are neither prac¬ 
tical nor advisable, may not be deprived of this valuable material, 
it is published by the School both in sets covering the several 
branches that it teaches, and in a series of single Home Study 
volumes treating of specialized lines of practical knowledge. This 
book is a sample of the make-up of the Home Study volumes and 
the titles and authors are shown on the following page. By this 
method the School broadens its field of activity; and from these 
sales it derives an income to use in general educational work. „ 
The School’s publications are clear and practical, and will 
be found ideal for reference and home reading. For those, how¬ 
ever, who desire more systematic study of the subjects in which 
they are particularly interested, the School advises a thorough 
course by correspondence as the quickest and surest means of 
obtaining the practical knowledge desired. 

The School offers correspondence instruction in all branches 
of architecture, civil engineering, college preparatory work, account¬ 
ing and business administration, drawing and design, electrical 
engineering, fire prevention and insurance, American law, mechan¬ 
ical, sanitary, and steam engineering, and textile manufacturing. 
It adapts its courses to the needs of the individual, by starting him 
where his previous education stopped, and giving him only such 
work as is necessary to fit him for the work he wants to do. 

On request the School will mail to any address a Bulletin 
containing full information regarding its courses and methods. 
It employs no representative other than its own publications. 

AMERICAN SCHOOL OF CORRESPONDENCE 

CHICAGO, U. S. A. 





American School of Correspondence 

PRACTICAL HANDBOOKS FOR HOME STUDY 


O WING to a constant and increasing demand for 
low-priced single volumes covering the sub¬ 
jects treated in the courses and cyclopedias 
of the American School of Correspondence, a 
series of practical handbooks have been com¬ 
piled to be sold through t'he Book Stores all over the 
world. If any purchaser finds that his local dealer does 
not carry the particular title which interests him, he 
can order direct from the publisher, who will make 
shipment on receipt of price. If, after five days’ exam¬ 
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purchaser may return it and his money will be promptly 
refunded. 


Partial List of Titles and Authors 


Alternating-Current Machinery_William Esty_$3.00 

Architectural Drawing and Lettering_Bourne-von Holst-Brown 1.50 

Bank Bookkeeping_Charles A. Sweetland_1.00 

Boiler Accessories_Walter S. Leland_1.00 

Bridge Engineering—Roof Trusses_Frank O. Dufour_3.00 

Building and Flying an Aeroplane_Charles B. Hayward_1.00 

Building Superintendence_Edward Nichols_1.50 

Business Management, Part I__James B. Griffith_1.50 

Business Management, Part II_Russell-Griffith_ 1.50 

Carpentry_Gilbert Townsend_1.50 

Care and Operation of Automobiles_Morris A. Hall_ 1.00 

Commercial Law___John A. Chamberlain_3.00 

Compressed Air_Lucius I. Wightman_1.00 

Contracts and Specifications_James C. Plant_ 1.00 

Corporation Accounts and the Voucher System. .James B. Griffith_1.00 

Cotton Spinning_Charles C. Hedrick_3.00 

Department Store Accounts_Charles A. Sweetland_1.50 

Descriptive Astronomy_Forest Ray Moulton_1.50 

Dynamo-Electric Machinery_ F. B. Crocker_1.50 

Electric Railways___Henry H. Norris_1.50 

The Electric Telegraph_Thom-Collins_1.00 







































Partial List of Titles and Authors — Continued 


Electric Wiring and Lighting_ r 

Estimating_ 

Factory Accounts_ 

Forging-'- 

Foundry Work_ 

Freehand and Perspective Drawing. 

The Gasoline Automobile_ 

Gas Engines and Producers_ 

Heating and Ventilation_ 

Highway Construction_ 

Hydraulic Engineering_ 

Insurance and Real Estate Accounts 

Knitting _ r __ _ 

Machine Design_ 

Machine-Shop Work_ 

Masonry and Reinforced Concrete _ 

Masonry Construction_ 

Mechanical Drawing_ 

Modern American Homes_ 

Motion Pictures_ 

The Orders_ 

Pattern Making_ 

Plumbing___i 

Power Stations and Transmission. _ 

Practical Aeronautics- 

Practical Bookkeeping--- 

Practical Lessons in Electricity_ 

Reinforced Concrete- 

Railroad Engineering-: 

Refrigeration__ 

Sewers and Drains_ 

Sheet Metal Work_ 

Stair-Building and Steel Square- 

Steam Boilers_ 

Steam Engines_ 

Steam Turbines_ 

Steel Construction_ 

Strength of Materials- 

Surveying--- 

Telephony--- 

Textile Chemistry and Dyeing- 

Textile Design_ 

Tool Making_ 

Valve Gears and Indicators- 

Water Supply- 

Weaving_ 

Wireless Telegraphy and Telephony 

Woolen and Worsted Finishing- 

Woolen and Worsted Spinning- 


PRICE 

. Knox-Shaad_$1.00 

Edward Nichols_ 1.00 

.Hathaway-Griffith_1.50 

.John Lord Bacon_ 1.00 

Wm. C. Stimpson_1.00 

.Everett-Lawrence_1.00 

Lougheed-Hall_2.00 

. Marks-Wyer_ 1.00 

Charles L. Hubbard_1.50 

Phillips-Byrne_1.00 

.Turneaure-Black_3.00 

.Charles A. Sweetland_1.50 

.M. A. Metcalf_3.00 

.Charles L. Griffin_ 1.50 

Frederick W. Turner_1.50 

.Webb-Gibson_3.00 

Phillips-Byrne_1.00 

.Ervin Kenison_1.00 

H. V. von Holst_3.00 

David S. Huffish_4.00 

Bourne-von Holst-Brown 3.00 

James Ritchey_1.00 

.Gray-Ball_ 1.50 

.Geo. C. Shaad_1.00 

Chas. B. Hayward_3.50 

James B. Griffith_1.50 

. Millikan-Knox-Crocker _ 1.50 

Webb-Gibson_1.00 

Walter Loring Webb_3.00 

. M. W. Arrowwood_1.00 

A. Marston_ 1.00 

William Neubecker_3.00 

Hodgson-Williams_1.00 

Newell-Dow_1.00 

L. V. Ludy- 1.00* 

Walter S. Leland_1.00 

E. A. Tucker_ 1.50 

Edward Rose Maurer_ 1.00 

Alfred E. Phillips_ 1.50 

Miller-McMeen_4.00 

Louis A. Olney__3.00 

Fenwick Umpleby_3.00 

Edward R. Markham_1.50 

L. V. Ludy_ 1.00 

Frederick E. Turneaure__ 1.00 

H. William Nelson_ 3.00 

Ashley-Hayward_1.00 

John F. Timmerman_3.00 

Miles Collins_3.00 








































































































































































































































































































































































